Attacking North Korea would result in millions of refugees pouring into South Korea and China. Nobody wants that

Hahaha, and what do you think's going to happen to Iran if this stuff is successful? They already have more refugees living there than in any other country in the world except Turkey [1], owing to US adventures in other parts of the world. And they have more than 3x the population of North Korea on top. For that matter they also have more than 3x the population of Syria.

[1] - https://en.wikipedia.org/wiki/List_of_sovereign_states_by_re...

If what stuff is successful?

The goal is to overthrow the Iranian government (again) and try to install a puppet regime (again). Conveniently enough, even if you happen to think the nuclear pretext is the goal - it still entails the exact same thing. Destroying some facilities is obviously not going to change their nuclear skills, capabilities, or ambitions. On the contrary - if there was internal doubt about developing a nuclear weapon within Iran, that doubt is now completely erased.

There was never any doubt about developing a nuclear weapon within Iran. You don't enrich to beyond 60% in a secretive bomb-proof bunker with any other goal in mind. This "oh now we've convinced them to build a bomb" line is nonsense.

They began enriching to 60% as a response to Israeli attacks on the country in 2021. Before that it was never higher than 20%. 60% is just below weapons grade and was meant to send a message. Similarly, the reasons their nuclear program is completely underground should be completely obvious at this point. Israel has been trying to get somebody to invade them for decades, has been assassinating anybody they can find, and so on.

Before this there was every reason to doubt Israel's claims, which they've been making for 30 years, about Iran imminently having a nuclear weapon. But at this point there's a practically 100% certainty that they will be aiming to create nuclear weapons as quickly as possible.

It's a gruesome thought, but I don't imagine very many refugees crossing the (heavily mined) DMZ into South Korea...