Why shouldn't Iran have a nuclear bomb? We do. We have more of these weapons from hell than any other nation.
What gives us the right to have the ultimate instruments of mass murder and then tell another country it can't? That isn't moral authority, it's bullying. Might makes right: the lowest moral common denominator.
If we had any actual moral authority, we would start dismantling our nuclear weapons, then challenge other nations to do likewise. Peace.