It isn’t a free service you’re paying a fee so their business gets what they want. That's where it should stop. If they’re supposed to make you anonymous you shouldn't give your ID to them. You shouldn’t have to give your ID for the right to use their anonymous services.
Last two words. A Service is called a Mixer by his definition unless they collect Know Your Customer type of information from ALL users.
Why the hell would I give my ID to a service whose purpose is to make me anonymous?