This is not in any way to say that gay adoption is a bad idea; the gay couples I know who have adopted are all ideal parents.I'm so on the fence on this issue of gay marriage and gay adoption. On the one hand I don't undertand any reason why it ought to be wrong. But it still strikes me that it is. And, as a Christian, I believe in the veracity of a bible that says it is.
But ignoring the moral platitudes, how can gay parents be ideal parents? I've commentted on this before. How can two gay men be ideal parents for (e.g.) a heterosexual girl? Where is the role model that the child has in her life? Or where is the appropriate role model for the heterosexual son of a lesbian couple?
That being said, I'm sure that the exercise of effective parenting skills is not endemic to heterosexual parents. But I think it's a far stretch to say that a gay couple can be an "ideal" parent. Ideally, children have role models in their lives and it strikes me that gay couples are very likely to be less than ideal.