Allow 'ban from group' option that would prevent banned avatars from joining 'open join' groups and from being invited to groups that are not open join. Include 'Ban members from this group' in the permissions settings under 'Membership' in group roles and responsibilities, so this power can be granted or denied by role. This will allow group owners to ensure that problem members are not able to return to groups, with the greatest advantage being to those who have 'open join' groups. Spammers, or others who abuse group privileges, can be blocked from accessing the group, without requiring that joining privileges be closed to others.