Unrestricted sense enjoyment is the cause of material encagement, but one who follows the rules and regulations of the revealed scriptures does not become entangled by the sense objects. For example, sex enjoyment is a necessity for the conditioned soul, and sex enjoyment is allowed under the license of marriage ties. According to scriptural injunctions, one is forbidden to engage in sex relationships with any women other than one's wife. All other women are to be considered as one's mother.
(Bhagavad-Gita--------3:34-------purport).

If one enjoys his senses unrestrictedly, he leads a sinful life. The animals do not violate the laws of nature. For example, the sex impulse in animals is very strong during certain months of the year. The lion is very powerful. He is a flesh-eater and is very strong, but he enjoys sex only once in a year. Similarly, according to religious injunctions a man is restricted to enjoy sex only once in a month, after the menstrual period of the wife, and if the wife is pregnant, he is not allowed sex life at all. That is the law for human beings. A man is allowed to keep more than one wife because he cannot enjoy sex when the wife is pregnant. If he wants to enjoy sex at such a time, he may go to another wife who is not pregnant. These are laws mentioned in the Manu-saṁhitā and other scriptures.
(Srimad Bhagavatam---------2:27:5-----------purport).

If one indulges in illicit sexual relations with another man's wife, that activity is considered identical with having sex with one's mother. This act is most sinful. The same principle holds for a woman also; if she enjoys sex with a man other than her husband, the act is tantamount to having sexual relations with her father or son. Illicit sex life is always forbidden, and any man or woman who indulges in it is punished in the manner described in this verse.
(Srimad Bhagavatam---------5:26:20-----------purport).

There are many learned sages, philosophers and transcendentalists who try to conquer the senses, but in spite of their endeavors, even the greatest of them sometimes fall victim to material sense enjoyment due to the agitated mind. Even Viśvāmitra, a great sage and perfect yogī, was misled by Menakā into sex enjoyment, although the yogī was endeavoring for sense control with severe types of penance and yoga practice. And, of course, there are so many similar instances in the history of the world. Therefore, it is very difficult to control the mind and senses without being fully Kṛṣṇa conscious. Without engaging the mind in Kṛṣṇa, one cannot cease such material engagements.
(Bhagavad-Gita--------2:60-------purport).

Today it has become a much advertised fashion for a woman to go almost naked, covering the lower part of her body only slightly, in order to draw the attention of a man to her private parts for sexual enjoyment. The intelligence engaged to attract a man to the lower part of the body is the intelligence of a professional prostitute. Similarly, the intelligence of a living entity who does not turn his attention toward Kṛṣṇa or the Kṛṣṇa consciousness movement simply changes dresses like a prostitute.
(Srimad Bhagavatam---------6:5:14-----------purport).

According to the Vedic system, therefore, before a child is conceived, the garbhādhāna-saṁskāra is performed. This ceremony molds the mentality of the father in such a way that when he plants his seed in the womb of his wife, he will beget a child whose mind will be completely saturated with a devotional attitude. At the present moment, however, there are no such garbhādhāna-saṁskāras, and therefore people generally have a lusty attitude when they beget children. Especially in this age of Kali, there are no garbhādhāna ceremonies; everyone enjoys sex with his wife like a cat or dog. Therefore according to śāstric injunctions, almost all the people of this age belong to the śūdra category.
(Srimad Bhagavatam---------5:2:2-----------purport).

The brahmacārī, or student, is never allowed to mingle with women and learn from the beginning of life about sex enjoyment. The basic flaw in modern civilization is that boys and girls are given freedom during school and college to enjoy sex life. Most of the children are varṇa-saṅkara, meaning "born of undesirable fathers and mothers." Consequently, the whole world is in chaos.
(Srimad Bhagavatam---------4:31:1-----------purport).

One cannot enjoy sex life daily at home or elsewhere and attend a so-called yoga class and thus become a yogī. One has to practice controlling the mind and avoiding all kinds of sense gratification, of which sex life is the chief.
(Bhagavad-Gita--------6:13-14-------purport).

A thief is put into the hell known as Sandaṁśa. A person who has sexual relations with a woman who is not to be enjoyed is put into the hell known as Taptasūrmi. A person who enjoys sexual relations with animals is put into the hell known as Vajrakaṇṭaka-śālmalī. A person born into an aristocratic or highly placed family but who does not act accordingly is put into the hellish trench of blood, pus and urine called the Vaitaraṇī River.
(Srimad Bhagavatam---------5:26---------summary).

There are restrictions for the householders even in sex life, which should only be engaged in for the propagation of children. If he does not require children, he should not enjoy sex life with his wife. Modern society enjoys sex life with contraceptive methods or more abominable methods to avoid the responsibility of children. This is not in the transcendental quality, but is demoniac. If anyone, even if he is a householder, wants to make progress in spiritual life, he must control his sex life and should not beget a child without the purpose of serving Kṛṣṇa.
(Bhagavad-Gita--------16:1-3-------purport).

In the brahmacārī life the training is sufficiently imparted so that one may understand that the world as property belongs to the Supreme Lord, the Personality of Godhead. No one, therefore, can claim to be the proprietor of anything in the world. Therefore, in the life of a householder, which is a sort of license for sex enjoyment, one must give in charity for the service of the Lord. Everyone's energy is generated or borrowed from the reservoir of energy of the Lord; therefore, the resultant actions of such energy must be given to the Lord in the shape of transcendental loving service for Him.
(Srimad Bhagavatam---------1:9:27-----------purport).

Man and woman both seek sexual enjoyment, and when they are united by the ritualistic ceremony of marriage, they are happy for some time, but finally there is dissension, and thus there are so many cases of separation and divorce. Although every man and woman is actually eager to enjoy life through sexual unity, the result is disunity and distress.
(Srimad Bhagavatam---------7:13:26-----------purport).

The materialist will argue that life in the tree and life in the man cannot be compared because the tree cannot enjoy life by eating palatable dishes or by enjoying sexual intercourse. In reply to this, the Bhāgavatam asks whether other animals like the dogs and hogs, living in the same village with human beings, do not eat and enjoy sexual life. The specific utterance of Śrīmad-Bhāgavatam in regard to "other animals" means that persons who are simply engaged in planning a better type of animal life consisting of eating, breathing and mating are also animals in the shape of human beings. A society of such polished animals cannot benefit suffering humanity, for an animal can easily harm another animal but rarely do good.
(Srimad Bhagavatam---------2:3:18-----------purport).

Materialistic life is full of thorns, and so one should live only by the prescribed method of Vedic regulations just to make the best use of a bad bargain. Life in the material world is maintained by sucking one's own blood. The central point of attraction for material enjoyment is sex life. To enjoy sex life is to suck one's own blood, and there is not much more to be explained in this connection.
(Srimad Bhagavatam---------2:3:19-----------purport).

The so-called advancement of human civilization has engaged a human being in the work of an ass. The laborers in great factories and workshops are also engaged in such burdensome work, and after working hard during the day, the poor laborer has to be again kicked by the fair sex, not only for sex enjoyment but also for so many household affairs.
(Srimad Bhagavatam---------2:3:19-----------purport).

A hog's life is degraded in its standard of happiness, which entails living in a filthy place, engaging in sex enjoyment at every opportune moment, and laboring hard in a struggle for existence, but this is unknown to the hog. Similarly, human beings who are unaware of the miseries of material existence and are happy in sex life and hard labor are the lowest of fools.
(Srimad Bhagavatam---------3:7:17-----------purport).

Sex life is the background of material existence. Here also it is repeated that demons are very fond of sex life. The more one is free from the desires for sex, the more he is promoted to the level of the demigods; the more one is inclined to enjoy sex, the more he is degraded to the level of demoniac life.
(Srimad Bhagavatam---------3:20:23-----------purport).

As early morning is the period for spiritual cultivation, the beginning of evening is the period for passion. Demoniac men are generally very fond of sex enjoyment; therefore they very much appreciate the approach of evening. The demons took the approach of the evening twilight to be a beautiful woman, and they began to adore her in various ways. They imagined the twilight to be a very beautiful woman with tinkling bangles on her feet, a girdle on her hips, and beautiful breasts, and for their sexual satisfaction they imagined the appearance of this beautiful girl before them.
(Srimad Bhagavatam---------3:20:29-----------purport).

The difference between material and spiritual enjoyment is that material enjoyment is limited. Even if a man engages in material sex enjoyment, he cannot enjoy it for long. But when the sex enjoyment is given up, then one can enter spiritual life, which is unending. In the Bhāgavatam (5.5.1) it is stated that brahma-saukhya, spiritual happiness, is ananta, unending. Foolish creatures are enamored by the beauty of matter and think that the enjoyment it offers is real, but actually that is not real enjoyment.
(Srimad Bhagavatam---------3:20:35-----------purport).

The more one can restrain the discharge of semen, the more one can be aloof from the problem of death. There are many yogīs living up to three hundred or seven hundred years by this process, and in the Bhāgavatam it is clearly stated that discharging semen is the cause of horrible death. The more one is addicted to sexual enjoyment, the more susceptible he is to a quick death.
(Srimad Bhagavatam---------3:26:57-----------purport).

In the lower grades of life (in plant and tree life) there is no system for sexual intercourse. In the upper grades (in the life of birds and bees) there is sex, but the insects and animals do not know how to actually enjoy sex life. In the human form of life, however, there is full knowledge of how to enjoy sex. Indeed, there are many so-called philosophers who give directions on how to enjoy sex life. There is even a science called kāma-śāstra, which is the science of sex.
(Srimad Bhagavatam---------3:25:38-----------purport).

The gṛhamedhī, however, who is interested only in sense gratification, does not follow any Vedic instruction. The gṛhamedhī engages himself as an advocate of sex life and also allows his sons and daughters to engage in sex and to be deprived of any glorious end in life. A gṛhastha enjoys sex life in this life as well as in the next, but a gṛhamedhī does not know what the next life is about because he is simply interested in sex in this life. On the whole, when one is too much inclined toward sex, he does not care for the transcendental spiritual life.
(Srimad Bhagavatam---------3:25:39-----------purport).

The hunting process is also carried on in a different way, as we have already explained. Hunting women, drinking different types of liquor, becoming intoxicated, killing animals and enjoying sex all serve as the basis of modern civilization.
(Srimad Bhagavatam---------3:26:9-----------purport).

A gṛhastha is not meant to enjoy sex life without restriction. Indeed, the whole purpose of Vedic life is to become free from sexual indulgence. All the āśramas are recognized for spiritual progress, and therefore although the gṛhastha-āśrama gives a kind of license for sex life for a certain time, it does not allow unrestricted sex life. Therefore, in gṛhastha life also, there is no illicit sex. A gṛhastha should not accept a woman for sexual enjoyment. Wasting semen is also illicit sex.
(Srimad Bhagavatam---------7:12-----------summary).