But don't children need both a mother and a father to be raised properly? (usually at least) Both parents play an important role in the child's mental development so you can't replace either with 2 parents of the same sex...
Just because heterosexual parents are the norm, doesn't mean that it's better.
I'd argue the opposite. Same sex parents have a harder time getting a child. A wanted child will probably fare better than a child conceived by two people that are culturally expected to breed.
So if a parent dies, what would have to happen according to you? Or if the parents are below a certain income? Or live in a bad area? Even if there was such a thing as an ideal parent or home situation, how many couples would fit that description do you think?