If you join a group or movement you should take responsibility for any action/wrong doing the group does as you did join them for a reason. You should have been well aware of the consequences before joining any group or movement whether for the good or for the bad. It's just a matter of someone owning up.. ^^
If you identify as a member of a group, you can't cherry pick what part you're a "real" part of. If you want to identify as a feminist, for example, that's great and all, but when other feminists act like complete idiots begging for superiority over men, you can't just brush it off and continue on your merry way being in the same group as people like that without others questioning why you're a part of that group.
We are all apart of some form of group or movement, socially or worldwide.
Taking Religion or Feminism for example as two very large communities worldwide, should you or would you be responsible for the actions that takes the group original positive idea and change it for the worst, harming or offending others.
This also includes extremists in any group and if you want to be apart of something that can change the way we think for the better, which can be both religion and feminism but stopped by the hatred and bigotry.
By taking responsibility, it doesn't have to be necessarily personal, but the responsibility you take as of joining a group, along with others help to prevent and change the hatred that occurs within the group.
This idea of responsibility, I think, should occur even in the minutest of group.
If a group is large enough that it has been broken down into chapters, if you will, then one chapter may go deviant and do something that reflects badly on the rest of your group. Look at any group that a fringe fanatic appears out of nowhere to side with. There they are, using reasoned arguments for their side, when this guy, who is identified with your movement, says something utterly inane. This reflects badly on you, and guess what example of you gets put up by your opposition. Bam, your credibility goes down the drain.