It's really that simple. Good legislation, like good food, movies, novels and pretty much everything else except for dogs (they're all good), is in the eye of the beholder. A politician or partisan who thinks a proposal is worth doing will think it's worth doing even if it increases the deficit. If he thinks a proposal is bad, he might argue that it's bad on the merits. But you can be sure that if it also increases the deficit, he will cite this fact as a major reason why it is bad.