I ran a meetup group with a few other co-organizers and it's amazing the amount of abuse people will take.
We had members that would come into the group, harass the rest of the members and continue with inappropriate behavior during our meetups.
We had one guy that would come in and basically corner any girl in the group and ask them out. During the meetup he looked like he wanted to hurt someone (he had angry looks on his face all the time), and wouldn't really talk to anyone or get to know the members.
After confronting the member, it continued. Since I was running the group with other people, I told them we needed to kick this guy out of the group. They outright refused. They felt that we shouldn't be exclusionary and that this would be 'mean'.
This guy eventually left when he was trying to get into an ivy league school and he sent us a blank entrance form and wanted us to fill it out for him. He sent us all angry emails and never came back.
I left the group shortly after this because I couldn't be part of a group that didn't protect its members.
More communities need to kick people out for inappropriate and harmful behavior.