Entirely different situation if Iran is allowed to develop nuclear weapons. Iran doesn't want Israel to exist, has the ability to affect world oil prices, and has supported world terrorism. In short, they cannot be allowed to develop nuclear weapons. There is no viable threat to them needing nukes for defense purposes, and they cannot be trusted not to strike Israel first. Israel had shown it can be trusted not to strike a Muslim country first with their nukes.
All Iran has to do is give full disclosure to the UN Inspection Agencies and they will be fine. Any deception could risk a possible consequence similar to Iraq. The leaders have Iraq as an example of how things can turn out in a tense political situation, so no need to play games with the Inspection Agencies.
A first strike by Israel could only be effective with US help. Israel would only put a dent in any Iranian nuclear weapons progress, and the tactical first strike could unite Muslim allies into a muti-natonal attack on Israel, terrorist strikes around the globe, and no doubt an attempt to close the Strait of Hormuz.
IMO, despite all these bad things that could happen.... if you think Iran is bad now, just keep letting them build nuclear weapons. At this point you make it extremely clear to Iran the consequences of any report that confirms moving in the direction of nuclear weapons development. If that line is crossed, then Israel should be given the green light to strike with full US support.
The questions are....is Israel prepared to defend itself in a conventional war? Is the world prepared for the increase in terrorist strikes, and to what extent will China & Russia get involved?
The whole situation outcome depends on Iran. Do you trust them to make a sane decision? However, do not underestimate the possibility of a false flag event against the US in the SofH to instigate and ignite this whole terrible situation.
Think About It