They genuinely can't understand the concept of standing up for someone because that someone stood up for you, even if you don't like him, respect him, or want anything to do with him.Vox's post reminded me of a story from when Mrs. Ipsa and I were first married.
I had a good friend that I used to hang out with. Mrs. Ipsa did not then, does not now and probably never will approve of this person. One day when she was frustrated with not understanding or liking my spending time with him she asked me why he was my friend.
Now here is the thing, every character flaw, bad behavior, etc she objected to was real. He really was all those negative things. I don't have an excuse for that. My answer was, "he is my friend because he is my friend".
That's it, that's the whole reason he is my friend is because he was my friend. I wasn't disowning him just because I got married.