From my many friends who are Democrats, I hear a common complaint: the Republican Party is a party of obstruction while the Democratic party is much more accommodating. Of course, the first reaction of most Republican would be to note the many not so accommodating actions of Democrats, from the attempt to filibuster Justice Samuel Alito to the refusal to negotiate any reforms in social security with the newly reelected George W. Bush. But such back and forth is pretty fruitless and may miss a more fundamental point.
It is not at all clear that it is rational for parties to engage in the same amount of obstruction. The rational amount of obstruction depends on how easy it is to repeal the policy being obstructed. If it is easy to repeal the policy, it does not make sense to pay the political price for obstruction, because the policy can be readily ended when the party comes to power. But if the policy is hard to repeal, obstruction becomes a more natural course.
Thus, the real question on the rationality and justification for obstruction is whether the Republican and Democratic parties face the same political terrain for repealing the legislation they oppose. And I do not believe they do, particularly when it comes to the creation or expansion of entitlements.