I think the concern is that some group will launch a dirty bomb at Israel, Israel will retaliate with nukes, and then the best case scenario is 'only' thousands dying. Oh, and did I mention that a dirty bomb can make a pretty large area uninhabitable for decades?

I mean Iran doesn't have nuclear weapons but they do have a nuclear program and it's very easy to go from there to nukes. Correct me if I'm wrong but AFAIK the principle behind nukes is pretty simple and it's modern geopolitics that makes them hard to get.

more than a few actors may (likely?) have very low yield devices. only takes a few to panic people and governments into stupid actions.