Yes, but contraceptives are not. Sex is natural, and child-birth is the natural consequence of sex. And it is also natural and healthy for a child to grow up in a stable environment where the parents share a commitment to each other.
The desire for sex is also natural. It stems originally from the spiritual world where it is found in its pure form, called adi-rasa. Material sex desire is natural for the material senses, but it is unnatural for the pure soul. It is the perverted reflection of the adi-rasa, contaminated by a covering of lust, the selfish desire to enjoy and imitate Krishna rather than to serve and satisfy Him.
"Therefore, O Arjuna, best of the Bhäratas, in the very beginning, curb this great symbol of sin [lust] by regulating the senses, and slay this destroyer of knowledge and self-realization." (Bhagavad-gita 3.41)
Materialistic society glorifies sex through its popular idols and advertising, while it plays down the obvious drawbacks. Devotees like to remain conscious of the drawbacks and glorify the saints who exercise self-restraint.
Materialists project the idea that sex makes you happy. If this were true, then prostitutes would be the happiest people in the world. Consider all the problems related to unrestrained sexual conduct and the benefits of celibacy and Vedic marriage.
Think of all the suffering that can be related to sex, for individuals and the society. And what is the true value of the pleasures one gains? Compare it to spiritual life.
The whole system of materialistic life revolves around this sexual pleasure. But this pleasure is like one drop of water in the desert. The desert requires an ocean of water. If you find one drop of water in a desert, you can certainly say, "Here is some water." But what is its value? Similarly, there is certainly some pleasure in sex life, but what is the value of that pleasure? Compared to the unlimited pleasure of Krishna consciousness, it is like one drop of water in the desert. Everyone is seeking unlimited pleasure, but no one is becoming satisfied. They are having sex in so many different ways, and the young girls walking on the street are almost naked. The whole society has become degraded. The men take advantage of the situation. There is a saying in Benga that "When milk is available in the marketplace, what is the use of keeping a cow?" So men are declining to keep a wife because sex is so cheap. They are deserting their families. (Srila Prabhupada, Journey of Self-Discovery 7.3)
"… the bodily demands begin with the tongue. If one can restrain the demands of the tongue by limiting its activities to the eating of prasada, the urges of the belly and the genitals can automatically be controlled." (Nectar of Instruction 1)
Eat moderately at regulated times and keep a balanced diet for good health. Eating for sense gratification at any time the tongue urges you will agitate the senses. Packing the belly up to capacity places pressure on the genital.
"While contemplating the objects of the senses, a person develops ttachment for them, and from such attachment lust develops…" (Bhagavad-gita 2.62)
Try this:
Do not think of a pink elephant with green spots!
Did you think of one? But I told you not to!
What do you think is the best way to avoid contemplating the opposite sex?
The restlessness or fickleness of the mind (mano-vega) is controlled when one can fix his mind on the lotus feet of Krishna.