Overzealous would be the right term, I think.
I have a friend who is convinced there will be some sort of apocolypse soon...particularly from economic meltdown. He doesn't go nuts, just got himself a big Ford Expedition, just in case...has a large supply of water bottles, just in case....and stockpiles canned food. (But not in quantities so large that it's out of hand)
The "doomsday preppers" on the other hand...while they've been around forever, and are just *now* getting attention thanks to the media, they're just kidding themselves.
Yes, there may be a big "doomsday" of some sorts soon. There are a million and one ways it could happen. There may also not be one for another 200 years. We can't know.
Going overboard like that is just plain silly - not to mention a waste of money. It's like wearing a big padded suit just in case you get hit by a bus, or wearing full kevlar to church in case some nut decides to open fire. Yeah, it might happen...but so might a million other things.