Yglesias clarifies his position:
[W]hen I say that pre-emptive fiscal adjustment is unlikely I meant precisely that: It’s unlikely, not undesirable. ... Given the number of veto points in the American political system, large change is always unlikely. Given a problem on which it’s viable to delay action, politicians will prefer to delay. It is possible to delay action on fiscal adjustment. And a complete fiscal adjustment would involve multiple large changes. Ergo, it’s unlikely to happen.