Yes, a nuclear Iran is intolerable and will undermine democracy in that country and region. Whenever a fascist regime gains nuclear capability, it only serves to undermine democracy because it creates fear in the hearts of the people. Democracy may thrive only when people feel safe and secure, as otherwise a fear to act occurs.
No, a nuclear Iran is not tolerable. A nuclear Iran undermines democracy, because a nuclear Iran would pose a constant threat. Iran has made many threats against the West and tolerating the fact that they have the capability would create a constant risk of a problem. The West would spend significant energies keeping Iran at bay, rather than focusing on domestic problems.