I don't think anything you do can help with this case. The problem is he likely won't be able to keep Life Link, and he won't let it go, to the point where he's even saying that the removal of it will ruin his characters.
How does he know homosexual marriage isn't allowed to begin with, did he asked Avenger? I don't think he did. Life Link isn't necessary to symbolize marriage, just say they got married, you don't need an ability to do that.
Whether he can keep Life Link or not, I don't know for sure. But I just want him to open up and accept the new RP for what it is. He shouldn't let himself be run by an absolute preference, it shouldn't matter what the RP is doing with it's abilities, as long as you can have fun with other people during said RP, isn't that the important thing?