Have you ever found yourself in a group setting (work or school and such) where there is a person that no one seems to like? Would you tell the person? What would be your hope and your motivation if you did?
I concur with the rest of the group. Nothing good usually ever comes from getting involved in situations like this...
Yes, particularly political groups. I have had occasion to tell one. It didn't do much good.
In my experience, telling "that" person they are that person (regardless of setting, reason or behavior) tends to invoke denial responses, demands for explanation and outright reinforcement of that behavior.
Better to live and let live. Keep in mind - All Relationships Are Optional. No one is forced to permanently stay in another's presence. Sartre not withstanding...