> signed up before we realized who they were, and then we would have to
> delete them "against their will" as opposed to simply not letting them
> join in the first place.  If I'm missing something here, please let me know.

I see little difference between "deleting against their will" and
"they may not subscribe unless we approve."  In both instances you
are saying A, C, E, and G may subscribe but  B, D, and F may not.

Whether you do it in advance or after the fact the result is the same.

Douglas