It's not about using nukes. It's about losing nukes. It's more likely that an Iranian nuke will go missing than for an American nuke to go missing. Even with the large number (too many, I think) that the US possesses.
Why is Iran any more dangerous with regard to loose nukes than Pakistan or North Korea? I'm against all nuclear proliferation, but I see no reason to single out Iran and to issue belligerent ultimatums, as all the Republican candidates with the exception of Ron Paul have.
If it weren't for Israeli warmongering and paranoia, we'd be far less concerned with Iran's WMD and far less likely to escalate the threats.