Quoting
cbg
The position you are taking limits the rights of one parent to make any decisions or take any action without the approval of the other parent. You're right; I don't approve of that kind of limit. It's one thing to be courteous; it's another thing altogether to to tell Parent A that they're not allowed to have their new spouse participate in the child's life in any way that Parent B has not authorized specifically, no matter what Parent A wants or finds convenient. That's hardly fair to Parent A and gives Parent B far too much power. We've seen plenty of examples right here of Parent B's who don't want Parent A, let alone Parent A's new spouse, to have any kind of authority whatsoever, for reasons that range from none at all to ridiculous. Some have had valid reasons, but most are frankly, just being selfish. I see no reason why Parent B should have that kind of control.
It's also unfair to the child, who will end up feeling as if they are the one making trouble. Children are self-centered little beasts, are very good at picking up emotions, and generally assume that they are the cause of any kind of conflict.