I could at least understand to some degree people who oppose same-sex parents adopting children, as it affects a third person.
No more than straight couples adopting a child.
I don’t know. What about the studies that say children fair better with straight couples than same-sex couples? (and yes I know there are straight couples that are abusive and of course I child would be better off with a non-abusive same sex couple than an abusive same sex couple) There are arguments that the parenting styles of mothers differ from that of fathers and that children benefit from the mixture of the two.