I don't claim to know whether he would use the nukes. I'm saying that it's possible for not knowing to be just as dangerous as knowing. You can model this with game theory. Put simply, if there's a 100% chance he'll send a weapon to Seoul (because he just did it, for example), but it's a small weapon with limited casualties you can assign some kind of number to how severe of a response that warrants. If there's a 20% chance he'll send a nuke and wipe out all of Seoul, a 60% chance he'll send a small weapon, and a 20% chance he'll do nothing, you can assign a number to that as well.
As for my personal feeling, I'm torn on whether or not a military conflict is warranted. But in my mind if you're not torn about it then you're not thinking hard enough. The "fuck it, just bomb them" people are ignoring the very real possibility of mass casualties in North Korea and the likely response by Pyongyang. The "fuck Trump, we're all gonna die" people are ignoring the very real risk of doing nothing and letting NK strike first.
It's all bad, and you should be torn about it. And I say this as someone who thinks the war in Iraq was one of the biggest failures of military strategy in recent history.