A valid question but I'm going to make the judgement call and say that opinions that take the form: "You should not do A because you are a member of group Y and

A valid question but I'm going to make the judgement call and say that opinions that take the form: "You should not do A because you are a member of group Y and Y's aren't good at or don't do A" are not okay. Your girlfriend was probably quite satisfied with a kitchen that had been promptly cleaned and that made her happy. However if she ever voiced the opinion, 'You should help me clean up', to your younger sister then that wouldn't seem okay to me.