are a big concern, not just in the west, but in the middle east region, where a nuclear-capable Iran would have a huge destabilising effect.
Ranting about using such weapons is one thing - actually doing so is another, and we shouldn't forget that any country which used nuclear weapons in anger would have to survive in what would then be a very cold world - you'll have few international friends the day after the bomb detonates. In fact you might not even be around; there are other countries with these weapons, and one fear is that a single detonation would spark a chain effect, with other nations panicked into attacking their nuclear neighbours.
It's all very complex, and it's to be hoped that underneath all the posturing Iran's leaders have calculated the odds correctly. Iran doesn't need to drop a bomb in order to raise the game - merely possessing such weapons would change the political power dynamic considerably.