Any time a person of marginal stability gets wrapped up in a religious, quasi-religious or fanatical idea they may decide that the ends justifies the means. ERGO, you have PETA terrorists, Eco-terrorists, right-wing ultra-conservative Jews in Israel who would rather see a cvil war in Israel than cede any settlements, die-hard commies, die-hard "Birchers", Jim Kopp (look him up, went to school with him), NAMBLA, the Panthers, the Klan, Aryan White partyites, etc, etc. Look at some of the "Grab yer guns, the world has ended and we need to man the barricades" postings we get here sometimes. Some of those guys may actually believe some of the stuff they post here. Or somebody may believe them and man his local barricades.
I'm sure there are some weak-minded left wingers that believe all the political crap they are being fed where 99+% of the population recognizes it as crap in a campaign, would one of them be animated enough to do it or try? just like there are some right-wingers who might fall into similar categories. Would one of them (either side) be motivated by political depression and ultimate pessism to commit an act of patriotic duty??