Q. Why are you against sex?
A. Because sex is similar to drugs, both in physical and social effects. It places primitive instincts higher than intellect, a human being - a sentient being - turns into a primitive animal. The system of priorities suffers deformation. This leads to many nasty perversions of all kinds, including socially dangerous ones.
It's not a mere coincidence that the most dirty words in any language are connected to sex, and that innocence and purity have always been synonyms for virginity.
Even without perversions, the urge to obtain a new dose of the "drug" forces people to all kinds of stupid mistakes, deception and crime. Sex often ruins friendship, stimulates lie and unfair play.
If the energy that the humanity wastes on the satisfaction of lust would be used in more valuable areas, the civilization would achieve much more success, and there would fewer destructive conflicts between individuals or social groups.
Besides that, sex is not as harmless for one's health as it is commonly believed, and can stimulate some disease, not all of which are infectious; there are even reports that sex can have a negative impact on lifespan. This is the practical side of the problem.
As far as higher matters are concerned, it can be added that sex (indulgence in primitive instincts) and improvement of one's personality are incompatible. Religion can provide even more reasons. Finally, copulation is aesthetically disgusting.
https://antisex.info/en/faqnew.htm