We cannot be the world's policeman. Rump, idiot boy, ran on that against jeb bush, remember? Trump criticized all the other GOP candidates for the same bullshit he's doing now.
I agree we cannot be the world's policemen. But if not us, who? If not now, when?
Letting that bunch who was running Iran ('Twelver" Shiites, who live to bring about the Apocalypse) get nuclear weapons to stick on delivery systems with increasing range just might not be a good idea. These are people who dream of being caught in some apocalyptic rapturous martyrdom at the end of the world when the 12th Imam comes crawling out of the well.
This is now.

With North Korea's help (which means China and perhaps the Russians), those circles could be significantly widened, but even without, the obvious economic effects on the world of that threat being utilized has far reaching consequences.
They need not conquer those resources, merely deny them to the rest of the world. If they decide to lend a hand to the Muslim invasion of Europe, capitals would be eliminated, not just a few targets here and there.
The more dead infidels, the merrier.
I do not think Trump has overstated the threat, rather his predecessors have understated it and kept it small by bribing the regime with resources it has used to grow its ability to be a regional or global threat.
Time to shut that down. The cold calculus of strategic planning will allow a number of "acceptable losses" to accomplish the mission. Sadly, that means gold stars for families, children who will never see their mother of father again, brothers and sisters absent from the family table. Such is the cost our military personnel have accepted, even to being the one who did not return, whether fighting hostile natives on the frontier, the world's premier army for independence, the imperial goals of Nazi Germany or Tojo's Japan, or smaller threats to stop them from becoming bigger problems.
Again, the question is one of "How many lives will be saved?" to be weighed against the predicted losses that will be avoided by every means possible but inaction, the one choice that would cost more.