A new perspective on Iran

Are there any rational reasons why Iran shouldn't be able to go nuclear, and I don't mean just for energy, I'm talking about weapons.

Of course the United States and other members of the nuclear club don't want Iran to get them. The more exclusive the club is the more power its members have.

Isn't this situation analogous to gun control in the sense that everybody should have the equal right to defend themselves? Either everyone should be able to carry a gun or no one. Obviously the US would say that Iran is a state that sponsors terrorism therefore they cannot be trusted. I'm sure the government of Iran believes the same thing about Washington. In reality the United States and its nukes are a much bigger threat to Iran then vice-versa.

The only reason for nuclear states to be so exclusive is to keep their military power and global hegemony. I personally don't want Iran to have nuclear weapons, but as a person with neutral citizenship, what rational arguments are there against Iran doing so?