Yeah, it's pretty funny (and scary!) how even Guests are an option to have full access to the control panel
Personally, I don't see any need to grant CP permission to anyone but Admins. I don't use "Global Moderator", personally, but maybe they'd be deserving of at least "Can edit users" as opposed to full CP access. (Not much in the CP would pertain to moderators anyway that I can think of...)