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I guess they could be. They've been together for about 6 years, Peter and I haven't even been together half of that, yet we live together and both our parents like the other partner. Whereas Alice's parents are from strong religious backgrounds, and don't know she is with Frank. It must be awful to them, but I still feel it is no reason to treat someone else badly.
I have had problems with other friends partners, but have never and wouldn't dream of saying something cruel, or putting them down just because I don't like them personally, it's up to you to choose your partner, not your friends.