It’s an inconvenience when a listing goes down for a half hr but what’s scary is it often gets used by the morons in Washington to say we got a ‘crisis’ that demands massive legislative action. Fortunately what happened w/ NASDAQ not too long ago never got anywhere but we’re still dealing with the messes the lawmakers spit out after Oct. ‘87, the dotcom in ‘00, and Oct. ‘08.
No 'legislative action' is required to correct this situation, either. SEC have plenary authority already to order the cessation of any form of mkt manipulation. No sane person can possibly argue that HFT is anything other than manipulation (well, HFT practitioners are probably sane enough, but I'm speaking of disinterested parties).