Earlier quoted context omitted.
It doesn't. Many people just dislike other people having sex (and this probably is natural). They can't say anything against people doing it in accordance with the standard but as soon as something doesn't fit in the puritan template they find an excuse.
People like sex. They don't accept public obscenity usually due to common sense objective realities, i.e. children being present. So there is this. And there is some more: as a dominant bdsm heterosexual person for some reason I don't feel an urge to present my sexual preference to the whole world all the time and demanding the public to accept it. Or even having it recognized as part of my "identity". Sex is sex, ha…
I accept this element of culture unconditionally and don't feel any interest in violating it so I am not going to expose children (mine or other) to sexual scenes ever.
However, although there may happen to be some (so why risk), I really fail to see reason behind it. Why is it considered bad for children to see people having sex? Especially when it's about non-violent "classic" sex between "normal" people loving each other and treating each other tenderly and not any kind of hardcore BDSM porn. I understand some particular kinds of sexual practices can seem weird and even shock some people yet what makes "vanilla" sex obscene and potentially harmful for a person (a kid or whoever) psyche is beyond my comprehension.
> I don't feel an urge to present my sexual preference to the whole world all the time and demanding the public to accept it. Or even having it recognized as part of my "identity". Sex is sex, happens in bed with my wife and is between us.
I support this point, yet...
... I was going to copy-paste-quote the next part but the message got flagged. The next was the question why seek others to be aware of your sexual preferences and accept them. I believe the answer is so they won't get "shocked" once they find out accidentally and nobody will be able to blackmail you. The the current state of culture makes it matter. Once everybody accepts everything is normal exposing your sexual preferences proactively will become irrelevant.