Austerity done correctly allows for a proper reset of spending, to fully understand what you should start spending on, and to keep the unnecessary expenses gone. Similar to how insolvency can revatalise a failing company (for instance, see hmv).
Our problem is that the state took a little bit from everything, but didn't actually have a proper audit of whether it was doing the right things, or doing them in the right way.
Keynes didn't just advocate spending during downturns, but saving during the good times. You perhaps need to look at your history if you think running deficits was what was done during the post war period...