I wouldn’t necessarily say that one side or the other is more apocalyptic or extreme because you can point to examples on both sides of the aisle. Just look at Dennis Kucinich if you think that’s not true.
I think the reason that the GOP seems to be more so than the other two is a matter of Political ideology. The Republican side seems to value confident assertions (regardless of actual fact) over the more traditionally Democratic approach of explaining the difference between the arguments.
This makes the Right appear to be more rigid and the Left to appear more pliant.
How you feel about this ultimately comes down to whether you take a nationalistic or global view of politics. For years, the US has been the world’s superpower, but power is transitory. As we move into a more multi-polar global environment, would you rather have bold assertions or honest dialogue?
What will benefit the US more in the long run?