Earlier quoted context omitted.
I don't think there's clear definition of what "harm" means, and for sure studies themselves can are are and will be hotly debated.
You explicitly said that a father could not replace a mother for sure , and now you are simply saying that the whole subject is "hotly debated"? If a child is worse off without having a mother or a father and does not get one of them, then such a suboptimal childhood (by your words) is definitely harmful , without having to resort to exotic interpretations of the word "harm". You had no problem denouncing that this s…
I just learned today about a gay couple that adopted a child and used him for child-porn and pedophile sex. Would I bring that up as an argument? No. Have I? No. It's not.
People DO have different views on what harming a child means. It's not a platitude at all.