That's a different story, as evidenced by the fact that you told a different story than the one I told.

If you're in a group and someone starts throwing stones at a cop, you help the cop get that person (at the very least by getting away from that person so you don't interfere with the cop). If you're in a group and a person joins the group and pulls out a Nazi flag, then you kick that person out of the group unless your group sympathizes with Nazis.