I take it you really don't know much about the doomsday clock. It's symbolic. It's supposed to represent how close humanity is to offing itself. And it's been around since 1947 so it's not exactly a new thing. As for "mad scientists", we're dealing with the board of directors for the Bulletin of the Atomic Scientists. This isn't exactly a bunch of random bloggers we're talking about.
I want to know how they will ever set the clock to midnight at the end of the world. Surely fiddling with a clock will be the last thing on anybody's mind when ten nukes are trained on your city or whatever. The whole thing is a waste of money.
One of these countries (Iran, N Korea, etc) uses one nuke, or sells one nuke to a terrorist organization which is then used, the response will be swift and tragic. What are they gonna do? Destroy one city? It isn't even Mutually Assured Destruction for them. It's simply Assured Destruction.
Ah. But wouldn't we destroy them all utterly even if they don't? I mean, I would say the reaction to 9/11 is pretty much an example of how we would react if N Korea or Iran nuked us, the amount of damage made aside.
Unlike the Mayan calender thing, this one is more symbolic from a group with a statement. Much like the people who actually believed in the Mayan calender deal, you apparently didn't read this carefully as said group is not much different from Occupy Wall Street (except with less crap in the mix of them.)