I'm not sure why people keep saying that Ben got banned for frequent complaining… that is not the case. He got banned for re-using the same ETCs on multiple bookings and exploiting a bug in the program, thus breaking its T&Cs.

The Supreme Court filing is interesting; and I don't doubt UA would be within its legal rights to terminate membership. That said, my question was whether there's ever been a report of United (not Northwest, a defunct airline) banning one of its members for frequently complaining.