If it "won't stop them" then there is no reason not to add this.
That is incorrect. If there is no harm, and there is a single (financial) benefit (and possibly others) then it should be added.
Or maybe the forum can gain "something by adding some fee." Anyways I make it clear above with an if.
Any extra money is surely welcome, and maybe theymos could hire more global moderators this time (i.e. promote more).