Is there a fundamental difference between Iran having nuclear weapons compared to Pakistan? If the government of Pakistan hasn't used them so far, then why would Iran?

If Iran has nuclear weapons, then its principal geopolitical rival, Saudi Arabia will want nuclear weapons. You have a proliferation risk that will greatly increase the risk of actual use of nuclear weapons.

I don't want anyone having those weapons. But they exist, and worse, old ones exist and are unaccounted for.

But who should judge which regime should have them, if only some should?

Most of us are born into a belief that our people are the best, the right people, and others may also be right... and many are wrong. But regardless, we are most right. As such, we often don't question some things. This is one of them.

So should we decide we are the best, most trustworthy holders of such technology and use just about any means to prevent others from getting the technology? However you narrate this, it is an ongoing history which visiting sentient beings would probably marvel at.

If Israel has nuclear weapons, then its principal geopolitical rival, Iran will want nuclear weapons. You have a proliferation risk that will greatly increase the risk of actual use of nuclear weapons.

/headagainstwall

In the case of Pakistan, the principal geopolitical rival is India. Despite the fact that both have nuclear arsenals and have had skirmishes over Kashmir, a couple of which after they both made public their nuclear capability, neither of them have tried to use those weapons.

What makes it any different if Saudi Arabia, Iran and Israel have them instead?

Iran is in an open state of warfare with Israel.

Dig a little.

Why?

Why is anyone at war with anyone else? Usually the answer is, "because they did this first". But if you follow all the trails, you ultimately come to the conclusion that the real answer is either, "well, they're not us". Or "they look different".

Or sadly amusingly, because "they claim they invented hummus, but WE invented hummus". Or "they wear their little caps differently from how we do".

But if you put two people from opposing sides together at a dinner table, or with musical instruments, or in a crisis situation, you may be surprised to see that they not only can get along but can become friends.

US companies used to put ads in US magazines bragging about how they were helping Iran build nuclear power plants.

http://2.bp.blogspot.com/-PFHs3qhA6Hs/TwxioL65IxI/AAAAAAAAEg...

Of course Iran had a secular, non-communist, anti-colonial parliament and government in the early 1950s. The UK and US supported the mullahs as a base and had Mossadegh overthrown and put a dictator in. The CIA then worked to help SAVAK kill off the secular left. In the late 1970s Iran cast off its colonial shackles, but as the US had empowered the mullahs and killed off the secular left, they took over.

The US and Israel have nuclear weapons. The US has waged nuclear war. The US was helping Iran become a nuclear power. Now that colonialism has ended, they can't pursue the nuclear energy the US and Europe and China have? The only nuclear power in the Middle East allowed is one mostly made up of non-Muslims, most of whom are not even from the Middle East but from the west?

Yet it’s ok for the US and Israel to have nuclear weapons, but others can’t have them?

You're presenting a false choice between OK and not-OK. In reality it's a spectrum.

I am less concerned about the prospect of South Korea having nukes than North Korea if we are forced to choose. And I am less concerned about Israel having nukes than Iran, given the genocidal intentions the latter has expressed combined with the fact it's a theocratic dictatorship make it less than guaranteed that the MAD doctrine would apply.

I'd much, much, much prefer for Israel to also not have nukes, but those two situations aren't equally as bad.