Sexual preferences that psychiatry considers mental disorders, like BDSM, fetishism and transvestism, or previously homosexuality and masturbation, usually have nothing to do with forcing anybody. Seems like much of psychiatry basically boils down to "we don't like this, so we consider it a mental disorder". As for the sexual stuff, I guess it comes from the old Christian idea that sex that is not for procreation is wrong, which is probably a result of agriculture. In an agricultural society, you want the maximum amount of children, I guess.

I find it fascinating that so many people are holding on to these obsolete beliefs (I mean, there are probably already too many people on this planet from an environmental point of view), although these beliefs do seem to gradually crumble as we speak.