Anonymous users see ads. Authenticated users don't. It costs $5 for an account.
They have run funding drives but, to date, $5/user keeps the lights on and provides a small crew of moderators each a modest stipend.
Edit: spelling, grammar.
When someone starts letting me pay for groceries with my browser history sign me up.
Would be like standing in the town square screaming your thoughts into a loud speaker then being upset that everyone knows what your thinking.
Good idea isn't it?