My very, very strong suspicion is that there has never been a time when there weren’t truly crazy people on all sides of the political spectrum doing their truly crazy things. Maybe 1% or so, or even 0.1% — which is a very large number, when you’re talking about a population of, say, 100 million. 

I tend to agree with this. There are some serious nut jobs in the US. The current media slant (not right or left, towards sensationalism) and internet availability combine to give them massive megaphones. Of course, as a Lefty, I think the conservatives wackos are much, much worse than the liberal ones. But I agree that the liberal ones EXIST, and in roughly similar numbers.