Thanks people

And the difference between the two hacks, after closer studies, is the fact that my hack can also email the users telling them that they have been deleted.
I value this feature because it would be annoying for an user to try to revisit if he remembers your forum at a later point, only to find his account terminated without explanation.
When I get home I will further improve this hack, by flagging the users for deletion, emailing them about the fate of their accounts, then after x amount of days (config), if the user still applies to the "flagged for deletion" groups, delete them (and optionally mail them about it).