Thanks for your reply Chris.
Actually I'm ok with the private group model as you have it, it's the public model that I feel would benefit by having the ability for the admin to both delete a user as well as delete/block. You support user deletion by the admin(s) of a public group, but there is nothing from preventing the same user from rejoining the group.
The objective of the addition above would be to enable groups to "block" non-members whom are appear to be joining hundreds of groups (here by view of their profile) so that they can dominate the group's leaderboard. Guess these folks, whom have nothing to do with our group, just like seeing their "name in lights".