Yes, Iran having nukes would be very concerning.
But not for the reason you think.
They may be crazy, but they're still smart enough to know that any nuclear launch by them would mean an immediate retaliatory strike against them that would be unsurvivable. North Korean is equally crazy but intelligent.
The true worry would be Iran supplying a small nuke to one of its client terror groups. Even so, Iran's smart enough to know that such a use by one of its proxies would be considered to be a direct nuclear strike BY Iran. Which would, once again, likely lead to a regime destroying retaliatory strike.
What really astounds me is how so few people truly learned the bitter lesson of European "diplomacy" post 1935.
OMG! We have to appease Germany or we might have another war! Besides, Hitler pinky swore that if we gave him this in response to his threats that he would be satisfied!
It's truly amazing just how well that worked out.
The ONLY viable response to rogue aggressor states is equal force, otherwise the aggressor state goes completely feral.
History has proven that time and time again. It just baffles me that so many people have been so failed by their primary school educations