Or (to use the old analogy of a UGC-based site as a nightclub/bar), they kick out people who have a bad enough rep and have pissed off enough customers that it

Or (to use the old analogy of a UGC-based site as a nightclub/bar), they kick out people who have a bad enough rep and have pissed off enough customers that it makes them look bad and might lose them money. I don't think they care - nor should they, really - about silencing this a-hole or another one for good. They just care about PR and business so they boot users who threaten that.