Owners of Community Groups should be able to bulk edit members of community groups. I have a community group set up for the entire middle school. As our students matriculated and enrollment changed from last year, I spent a couple of hours removing every single student member one at a time (and confirming each one), then adding the new students and re-adding some of the current students one at a time. Adding without bulk is not quite as bad, but it would make it soooo much faster to have boxes to checkmark next to each current member of the group or potential member of the group- would have cut the work down from hours to minutes.
I had a similar problem and a quick workaround was to change membership type via OnCampus > Procedure > Community > and under Add/Edit Community Group, edit the group, and change the membership type on the left. Taking these steps made it possible to quickly purge the roster and I was then able to change the type back and begin rebuilding the roster.