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.