Because Iran has sworn to destroy them.

You can describe the process as emotionally as you want, Israel and the west are key stakeholders - with the means to deny, prevent, and obliterate whatever they choose.

Nuclear weapons are not a rite of passage - they are a means to both defend a country and provide cover for aggression. The latter is the concern.

Have you seen the past 70 years of international law, international relations or how civilized society handles literally everything?

Why would Israel / the west allow a nation who has sworn the destruction of another to gain nuclear weapons capability? Especially when it is within their means to deny them?

Iran can attempt to pick up whatever stick it wants- and Israel / the west can deploy theirs whenever they choose as well.

Is it fair? That’s the wrong question to ask. The actual question that should be asked is - what will they do with it if they get it? What are the consequences of a nuclear Iran? We share this world, and like it or not big sticks matter, as do the opinions and interests of our neighbours.

They shouldn’t because the west said so and will bomb them into oblivion if they do.