If you think that the debt limit is an important concept for limiting deficit spending, why do you think that it should always be increased?

I never said that. I believe that screwing with it without an appreciation for the complexity of the system one is trying to improve upon can have dire consequences. And the purpose of this discussion is to see how to protect one's self from these consequences.

The debt limit is actually pretty ineffectual at limiting spending, and now we've again been reminded that it can be exploited. But unconditionally making debt-limit increases automatic would sent the wrong message to legislators and investors. I think a balanced budget amendment would be a much better alternative.