Uncheck checkboxes with form submission

I'd like to have contacts be able to manage their own list segments, and the best user interface with this in the available form fields is checkboxes.

But apparently form submissions can ONLY check checkboxes....they can't uncheck them!

Please make a function to allow contacts to check and uncheck checkboxes and have the changes reflected in their contact record. "List Selection" forms are ugly and no one knows how to use them to select multiple things....

Thanks!!