Societies can not have rights, as society is nothing but many people. People have rights, but I don't see how many people can have the right to regulate somebody's private behavior. Where would such right come from? Why do you think I have the right to tell you what you can and can not do, even if it doesn't concern me at the least? Why do you make special emphasis on sex - why do you think I have the right to say how you can have sex? Sex is one of the most private affairs in our culture - why do you think it is especially appropriate for me to intervene in it when you engage in it without my participation?
>Societies can not have rights, as society is nothing but many people
This is pedantry. The many people that comprise a society hold in aggregate the ability to enforce rules that ensure their survival and prosperity. This is the basis of all governance.
>Where would such right come from?
Governments derive their powers from the consent of the governed, regardless of the institution that governs. The right comes from the unified concurrence that some behaviors are dangerous to social survival, and the unified strength to enforce that concurrence.
>Why do you think I have the right to tell you what you can and can not do, even if it doesn't concern me at the least?
See above. The government has the right to forbid behavior insofar as the people believe that behavior to be detrimental to their survival.
>Why do you make special emphasis on sex - why do you think I have the right to say how you can have sex? Sex is one of the most private affairs in our culture - why do you think it is especially appropriate for me to intervene in it when you engage in it without my participation?
I put special emphasis on sex because sex carries very unique properties. Sex is the only mechanism by which a child can be conceived, which roots it directly in the core of a society's concern -- their perpetuation, their survival is directly impacted by sexual practices.
Furthermore, most people have very strong sexual instincts and impulses that are evolutionary necessities, but are threatening to social survival if they are not checked by the aggregate behavioral standards of the populace. Some people have powerful violent impulses, but not most people. Some people have powerful psychotic impulses, but not most people. Sex is special because almost everyone has overpowering instinctual responses to sex, and sexual behaviors or displays therefore demand special control and attention from the governing authority.
Sex is super great and everything, I'm not saying it's bad. I'm just saying it's dangerous as well as necessary and pleasant. Rules must be established to ensure that the dangerous side of the coin sees minimal face time.