Megan McArdle on debt crises:

As I think I've said before, I used to cover financial crises (from America) and wonder why governments didn't do things that seemed so obvious.  The answer, I now realize, is that politicians can't just do the "obvious best" thing.  There is no such thing as a perfect rational maximizer in policymaking.

Politicians are always limited by what their voters think is fair.  The voters may be right, they may be wrong, but in the end (hopefully), they're still the boss.