It really is simple.
The Conservative line is that Iran is a bad thing. Period. It is the biggest obstacle to US hegemony in the Middle East and probably the ultimate prize sought by the Bush Administration. And Iran has been severely abused by American for a long, long time.
The US is working very hard to box them in, Afghanistan on one side, Iraq on the other. Besides that, it's a Muslim country with oil, and you don't want them Muslims to have any money.
Ironically, it's probably the biggest and only winner in the $2 trillion war Bush is fighting.
Arf