I doubt if that is actually the case though.
But I think the 'stable family arrangement' factor weighs heavily in all this. And elsewhere in this thread I think I've shown that there can be pressure on a child simply because it is raised by two gay parents, after all, it immediately makes you the odd one out. Of course other children should be brought up to realize that it makes no difference as far as the child is concerned, but unfortunately that is not the case.
Teenagers that are gay as a rule do what they can to stay under water in plenty of cases for fear of the kind of nastiness that can come out of being 'out' at a young age. Not all schools deal with stuff like that well - in fact, most schools don't.
Long term stability is one of the very important aspects of the quality of parenting, but it's not all of them.
In fact long term stability is itself determined to some extent by the nature of the relationships between each parent and the child or children.
The point of my question was to help each person who wants to think about this issue clarify their ideas by asking themselves whether it's the nature of the relationship between the "parents" that's the issue, or whether it just matters that there is some sort of strong bond, whatever that may be.
I'm not trying to lead anyone to on conclusion or other, just point out a thought experiment that might help people understand their own points of view.
Would you allow a pair of people who are not in a relationship to adopt, for example, two great friends who just happen to live together, but are not in a sexual or romantic relationship with each other?