Yes, I agree, too, it should be mostly about the children, not the adults. There's a problem, however, I think, because the "best interests of the child" aren't always so clear. A GP may not be what one would call "abusive," but if they often badmouth the mom or dad or criticize their rules in front of the child, that could damage the child's respect for their parents. That, in turn, could hurt the parent/child relationship, which clearly isn't good for the child. A judge might not be able to predict those longterm effects, but they still might be there.
On the other hand, just because both parents agree that a certain GP shouldn't see a child doesn't mean they're right, IMO. They could both be vindictive, petty or just wrong. Also, one could just be going along to get along with the other. Unfortunately, since these issues aren't always so black and white, I guess the courts need some kind of basic standard to go by, and the idea of supporting a decision made by two fit parents probably makes sense, even though it can end up hurting some good, loving GPs. I just don't know how that problem could be solved.
I definitely agree that it has to be a case-by-case thing. What works for one family isn't necessarily going to work for another.
It's just such a shame such cases have to exist at all. Though I'm not in this kind of situation, I know that "there but for fortune, etc." So I really hope they find better ways to resolve these very sad problems.