The problem with the arms-race argument here is that it implies that just because an arms race is inevitable that the only acceptable course of action is total capitulation. Twitter is bigger than any of the botters, and if it wanted it could raise the cost of entry of botting high enough that nobody would be able to afford the bots in any quantity large enough to make a difference. They just simply don't want to.

(As for false positives, I've seen plenty of people whose accounts were suspended for reasons unclear to them; Twitter seems to care very little whether its captive userbase is pissed off or not.)