Though even then I don't think its certain Iran would become more aggressive and seek to start destructive conflicts. I think it could be just as easily the case that obtaining nuclear weapons moderates Iran's militaristic efforts. If they aren't willing to use their nuclear weapons to directly strike Israel, then that suggests they don't want to risk being attacked themselves. The same logic of not wanting to risk nuclear destruction would arise if Iran started a conventional war with Israel. And the political science literature shows that when two nuclear powers engage in conflict with each other they are very cautious to escalate things. Two examples off the top of my head are the US/Soviet conflict and the India/Pakistan conflict.
Andrew adds another example of a country moderating after getting nukes:
Since China's adoption of nuclear status, it has actually behaved more responsibly abroad, not less. Jon makes a very persuasive case that nuclear weapons really don't give countries much of an edge, and, if anything, tend to calm them down, especially is they are in a region where they have foes who do have such weapons.
Ron Paul is the only candidate that seems to understand this. I'm not exactly sure how his policy would play out. But he seems willing to not provoke Iran, unlike Obama, and allow them to obtain nukes. You can disagree with that or be a bit weary of could happen if an accident were to occur, which I am. But it suggests to me that Paul has given the issue some thought and that he doesn't hold the same deranged sense of American (and Israeli) superiority that the rest of this country does.
This is why Paul is getting so much play on political blogs. These are the ideas that so many liberals, libertarians, and conservatives want implemented. And they are the ones that Obama is ignoring and outright repudiating. It still seems unlikely, but I wish Paul could win the Republican nominee so that we could see him debate these issues with Obama.