The problem is the endless extortion attempts that will follow. i.e. pay us lots of money or we nuke LA. The US really needs to deploy its anti missile tech and demonstrate to NK that any missile it shoots will be shot down.
How will "pay us lots of money or we nuke LA" work if the US can just say "do it and we'll nuke every city in North Korea 10 times"? Mutually assured destruction has kept us all alive the last 60-70 years.