You should be able to be banned from a specific thread. Say, if you are making non constructive posts or being annoying, but nothing ban worthy, then your posts in that thread are hidden and you are unable to post in it anymore. Being banned from 3 threads results in a ban.
Waddayathink
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..or just get banned in one, which means you'd be banned from all the threads. Otherwise you won't "learn your lesson". (Not that many members do).