Megan McArdle says to think of it as insurance:

Austerity is an expensive form of insurance against a true fiscal crisis. And though it doesn’t necessarily seem like it when you’re not having one, fiscal crises are much, much worse than austerity budgets. Fiscal crisis means that rather than unpleasant cuts, you have sudden, unmanageable collapses in things like public pension plans. The resulting suffering is not unpleasant; it is disastrous.
A year or two ago, I’m sure some corporate executive at BP was asking why the company would consider installing expensive remote control valves on its offshore rigs, when this sort of spill is extremely rare, and the fail-safe might not even work. One could even argue that given the economic cost of higher gasoline prices, and the rarity of these spills, BP made a good bet. We might well . . . if the spill hadn’t happened.
But once it has, we’re damn sure that we wanted them to be a lot more careful, no matter what the cost.