[x-factor]

Should Iran be treated as an enemy? Yes. Certainly their national aims and ours are in conflict.

Should this conflict with Iran be treated as a zero-sum game? No.

I don't think Iran meets any of my criteria fully.

1) Are they violent? Yes, but not as a matter of philosophy. By that I mean, that mass violence isn't a goal in and of itself for them. If that were the case the world would look even worse than it already does.
2) Even the hardliners don't reject compromise completely out of hand.
3) Aggressively expansionist? Right now? Yes, because they have an excellent geopolitical opportunity. As a matter of philosopy? No.

Adversarial though they may be, they are not exceedingly violent and, as tk27 noted, they are not beyond reason and negotiation. Furthermore, the Iranian government (much less the Iranian nation) is not at all a monolith. Ahmadinejad and the hardline faction talk like maniacs, but they're constrained by other factors, the populace chief among them.

Persians are an educated, cosmopolitan people. They've got garage bands and blue jeans, and the women are smoking hot under the veils they're forced to wear. A little time and a little pressure and Iran I think Iran will come around of its own.

Thats not to say they're not a threat. Iran should be aggressively contained and their government undermined through all sensible means. We should view it as basically a regional cold war. Iran needs to be slowly and methodically strangled...throwing haymakers is just going to cause more and bigger problems.