And his reasons are straightforward:

They are arbitrary and beg to be gamed. It is irresponsible to make one that is absolutely unbreakable, even in the face of an economic depression or other national catastrophe. Yet even the most well-intended exception will open the door to wholesale abuse.

That sounds about right. I worry that they encourage off-balance-sheet activities, like credit guarantees and other easily concealed forms of spending. I do think relatively easy-to-override, well-designed caps at the state level can play a constructive role, e.g., caps that factor in population growth, etc., as they can serve as a useful stumbling block in flush periods. But federal caps are all too often about deferring tough decisions.