The real fact is that naturally every living species were made to reproduce. By going into a homosexual act, the species doesn't reproduce. So it's an unnatural act.
However, homosexual relations have been practiced very long now, so they're just another part of the society that we live in. Just as there are the rich and the poor.
Homosexuals are not even near to pedophiles, and it's pretty damn idiotic to compare them. Homosexuals do not molest and force the other person into having sex with them(of course there is the thing called rape, but heterosexuals also have it).
By denying homosexuals to get married, you won't change anything. They won't disappear. And if a child is raised normally, I don't think there's anything wrong with an orphan to be raised in a family than being raised in an orphanage.