(Click to enlarge photo of Srila Prabhupada performing a marriage ceremony, Boston, 1969)
"In Bhagavad-gītā (BG 7.11) it is said: dharmāviruddho bhūteṣu kāmo 'smi bharatarṣabha. Sex is allowed only for the begetting of children, not for enjoyment. One can indulge in sex to beget a good child for the benefit of the family, society and world. Otherwise, sex is against the rules and regulations of religious life. A materialistic person does not believe that everything is managed in nature, and he does not know that if one does something wrong, he is witnessed by different demigods. A person enjoys illicit sex, and due to his blind, lusty desire, he thinks that no one can see him, but this illicit sex is thoroughly observed by the agents of the Supreme Personality of Godhead. Therefore the person is punished in so many ways. Presently in Kali-yuga there are many pregnancies due to illicit sex, and sometimes abortions ensue. These sinful activities are witnessed by the agents of the Supreme Personality of Godhead, and a man and woman who create such a situation are punished in the future by the stringent laws of material nature (daivī hy eṣā guṇa-mayī mama māyā duratyayā [BG 7.14]). Illicit sex is never excused, and those who indulge in it are punished life after life. As confirmed in Bhagavad-gītā (BG 16.20):
āsurīṁ yonim āpannā
mūḍhā janmani janmani
mām aprāpyaiva kaunteya
tato yānty adhamāṁ gatim
'Attaining repeated birth among the species of demoniac life, such persons can never approach Me. Gradually they sink down to the most abominable type of existence.'
The Supreme Personality of Godhead does not allow anyone to act against the stringent laws of material nature; therefore illicit sex is punished life after life. Illicit sex creates pregnancies, and these unwanted pregnancies lead to abortion. Those involved become implicated in these sins, so much so that they are punished in the same way the next life. Thus in the next life they also enter the womb of a mother and are killed in the same way. All these things can be avoided by remaining on the transcendental platform of Kṛṣṇa consciousness. In this way one does not commit sinful activity. Illicit sex is the most prominent sin due to lusty desire. When one associates with the mode of passion, he is implicated in suffering life after life."
(Śrīmad-Bhāgavatam 5.14.9, Purport)
"Indulgence in sex life by a man or woman living single is never acceptable in human society. A man should strictly follow the principles of brahmacārī life or, with the permission of the spiritual master, should get married. Single life with illicit sex is animal life, for the animals have no such institution as marriage.
Modern society does not aim at fulfilling the mission of human life, which is to go back home, back to Godhead. To fulfill this mission, the system of varṇa and āśrama must be followed. When the system is followed rigidly and consciously, it fulfills this mission, but when followed indirectly, without the guidance of superior authority, it simply creates a disturbing condition in human society, and there is no peace and prosperity."
(Kṛṣṇa Book, Chapter 80)
"Materialistic life is based on sex life. The existence of all the materialistic people, who are undergoing severe tribulation in the struggle for existence, is based on sex. Therefore, in the Vedic civilization sex life is allowed only in a restricted way; it is for the married couple and only for begetting children. But when sex life is indulged in for sense gratification illegally and illicitly, both the man and the woman await severe punishment in this world or after death. In this world also they are punished by virulent diseases like syphilis and gonorrhea, and in the next life, as we see in this passage of Śrīmad-Bhāgavatam, they are put into different kinds of hellish conditions to suffer."
(Śrīmad-Bhāgavatam 3.20.28, Purport)
"So instead of becoming sinful, to become pious, you simply follow these four regulative principles. The first principle is illicit sex. That is forbidden. Sex is not forbidden, but illicit sex is forbidden. That is not very difficult. Everyone wants. That is the necessity of the body, that sex. As we want to eat, as we want to sleep, similarly, there is sex desire. But if you want to become first-class man, then don't have illicit sex. Except marriage, do not have sex. The human society...
Therefore, human society, there is marriage. There is no marriage in the dog society. So therefore, sex life within marriage and regulative principle, that is not prohibited. That means anyone who follows these rules and regulation, he becomes purified and pious. Without becoming purified and pious, you cannot understand God. It is said therefore in the Bhagavad-gītā,
yeṣāṁ tv anta-gataṁ pāpaṁ
bhajante māṁ dṛḍha-vratāḥ
A person who is completely free from sinful activities, such person can become a devotee, a lover of God. So this Kṛṣṇa consciousness movement is teaching to the human society how to become purified. There is no such restriction that 'This man can be purified; that man cannot be.' No, there is nothing like that. Everyone can be purified if he desires to be so. So immediately we may not be able to purify. As it is prescribed—no illicit sex, no meat-eating, no gambling, no intoxication—it may not be possible because those who are accustomed, it is difficult to give up. Therefore the process is given very simple: 'Chant Hare Kṛṣṇa.' So purification is absolute. That is necessary. Without purification, you cannot understand God. But the method we are prescribing... Not we are prescribing; it is Caitanya Mahāprabhu's prescription. We are simply propagating that 'Chant Hare Kṛṣṇa.' Yes."
(Srila Prabhupada Lecture, Mexico, February 12, 1975)
"We don't prohibit sex, but illicit sex is most sinful. Most sinful. Unfortunately, they are so rascals, one sex to another, another sex to another, another sex... That is māyā's illusion, influence. But if you stick to Kṛṣṇa... Mām eva ye prapadyante māyām etāṁ taranti te (BG 7.14). If you catch up Kṛṣṇa's lotus feet very tightly, then you will not fall down. But if you make a show of so-called brahmacārī, so-called gṛhastha or so-called sannyāsī, then you will fall down. We are experiencing that. Then you must fall down. Kṛṣṇa will not tolerate a defaulter, a pseudo devotee."
(Srila Prabhupada Lecture, Los Angeles, January 5, 1974)