I'm pretty sure the US public would require retaliation in the event of, say, a prolonged regional blackout, a breached dam, a meltdown at a nuclear facility or any other number of real world insanity caused by a cyber attack.

"for no reason" I'm sure there are reasons. LulzSec does it for the "lulz". China has their own reasons, whatever they are they are and we can sit and discuss them but there needs to be red lines. Figuring those reasons out does not mean we should not have a well known military posture in certain eventualities.