There is an excellent, thought provoking piece on the Guardian's website by Mehdi Hasan "If you lived in Iran, wouldn't you want the nuclear bomb?"
Mehdi makes a very logical case, Iran is basically encircled by either the US's allies, countries the US are currently occupying/have a strong military force, or nuclear armed countries. Also there is the potential nuclear power Israel just a missile launch away. If you back someone into a corner then they are likely to want to fight back or at least have the ability to if pressed.
He makes the valid point that Iraq, Afghanistan, Libya etc have faced military intervention from the West over recent years, yet North Korea who have small nuclear capability have not (now I'm not saying that this is the sole reason why not but it may be a contributing factor). By obtaining nuclear weapons Iran would have a real deterrent against any action from a foreign country. There has been so much heated talk between themselves and Israel that I doubt anyone in that region feels that peace between the two countries should be taken for granted.
Personally I am massively against nuclear weapons. If it were up to me the first thing that would have been scrapped in the comprehensive spending review last year would have been Trident. One of the reasons for having it is apparently to stop blackmail from nuclear armed states as we would have the ability to retaliate. Surely this could therefore be applied to Iran, a state much more likely to face pressures from nuclear armed states.
I think it is massively hypocritical for countries who have nuclear warheads to then turn around to other countries and say that we need these to protect ourselves but you can't have them. As such it is perfectly understandable that they would feel threatened by this and would want similar capabilities themselves should a situation come up where they require them.
Unfortunately we can't uninvent the nuclear bomb so we should accept the fact that other countries are going to want their own nuclear capabilities to go alongside those of the USA, Russia, UK, France and China as well as India, Pakistan, North Korea (?) and Israel (?). At the end of the day though, there aren't too many conflicts as bad as India and Pakistan have been and they have both got the weapons without it ending up in a catastrophe. It is a sad day whenever any country obtains the ability to slaughter large numbers of innocent people on mass, but when faced with the prospect that it could happen to them it is only logical and natural that they would want their own deterrent.