Keg, the only reason your opposite-sex marriage ideal exists is because it's traditional. What about societies where kids are raised collectively? What about families where there are a dozen or more kids as there were in the past. You can't tell any of those kids received much in the way of individual love and attention from their parents.
On what basis are you claiming same-sex parents are any worse than having opposite-sex parents at bringing up kids in a loving and supportive environment?