mikhail said:
It's quite reasonable. Adoption affects a third party - the child.
Anyone ever seen a study on the effects of having a gay couple as your parents? I'd be quite interested in reading one.
[disclaimer: not saying I'm for or against here, just looking for info.]
Funnily enough I've recently read interviews with children adopted by lesbians in a Dutch newspaper (because it was X years ago since it was allowed). They were all in their teens or early 20s, all of them seemed like average people to me.
Most of them did have problems with having no father and two mothers during puberty though, and especially explaining that time and time again, one even made up a story about his father having died in a car crash and kept that story throughout his entire high school career!
So having gay adoption parents probably does influence the children. But then again, having idiots as adoption parents probably influences them as well. While gay marriage is legal, and adoption by marrieds is legal, I don't see a reason to disallow it.