As long as Israel is not disarmed of nukes, there is no reason why Iran should not be allowed to have them. Its pretty stupid letting Israel with a population of only a few thousand to be dominating the whole of the ME.
I trust Israel more than I trust Iran (which is already little). I can give one reason why Iran shouldn't have nuclear weapons: religious fanaticism and its hatred for Israel and apostates (and non-muslims). Not all of Iran is anti-west, but its govt. is ruled by a theocracy which has made no secret of its hatred against Israel. I am not persuaded that when religion and fanaticsm are together that rational decisions can be made, especially with regards to nuclear weapons. I sincerely doubt that radiation for several thousand years will deter their willingness to use nuclear weapons on Israel.
Why should Iran not be able to secure its sovereignity with nuclear weapons?
Religious fanaticism
I see no reason why Iran should not be allowed to have nukes especially when Israel, India and Pakistan already have them. If the USA real wants to rid Iran of nukes, it must create an example by disarming Israel first!
The US wasn't successful in preventing India and Pakistan from being able to produce nuclear weapons, and I'm somewhat nervous about Israel's possession of nuclear weapons. But I am more certain that Israel will behave rationally and be mindful of MAD (mutually assured destruction) than religious fanatics controlling Iran. It's also easier to prevent pandora's box from opening up than to try to put the genie back in the bottle.
Also to OP:
Radical Islam is indeed a threat to the non-muslim world. Notice I said radical. I have no doubt that most law-abiding muslims may recoil at Western culture but are willing to live in peace as long as they can practice Islam by themselves. The fundamentalists, however, see the world as either muslim (good) or non-muslim (bad). What 9/11 demonstrated was the willingness of fanatics to kill innocent civilians and to strike fear and terror.
It may be an opinion, but unlike you, I take seriously Bin Laden and Al Queda's threats. Their actions have demonstrated time and time again that they are not just mouthing off, they are serious and willing to murder innocents to fulfill their delusions of grandeur (ie caliphate in the ME).
As for the second part of your response, Islam as it stands can co-exist with the West. I do not accept the belief of radical fundamentalists that there is an inevitable clash with Christianity and other religions and/or Western civilization. But I do believe that these Islamic fundamentalists pose enough of a threat to be taken seriously, and to be dealt with.