I think you should enable users to cancel their membership.

but with limitations:
- postings should stay
- username should stay blocked, to prevent imposters
- banned users should not be able to delete their membership, because we don't want them to be abuse this method to reregister with the same email address.

basically, you could handle this as "self banning", only that friendly users should be able to re-use their email address.

flint
flint@poisonfree.com