It's almost certainly an underestimate. If an account is gone that's a permanent ban, and they issue temp bans all the time for all kinds of retarded reasons. There was even a thread calling for even longer bans for "bigots". The proportion of users who have been been subject to some kind of ban at some point is probably north of 90%. I'd be curious to know how many just don't come back after being subject to a temp ban imposed for bullshit reasons.

It's almost certainly an underestimate. If an account is gone that's a permanent ban, and they issue temp bans all the time for all kinds of retarded reasons. The proportion of users who have been been subject to some kind of ban at some point is probably north of 90%.