I suppose that is another possible solution - delete the autologin user. However, I have a bad feeling about that solution ;-)
Here’s part of the reason why:
Before you delete that user, make sure that your new admin user (which is to say, a user in the adm group) has all sudo (probably still with password) permissions…. You don’t want to end up with a machine that you have to boot on a live DVD in order to become root!