Left-wing kooks are no different than the right wing kind, just their issues are different. Instead of global warming, they are anti-vaccine, instead of human embryonic stem cells, they are anti-agriculture.
One way fringe kooks on the left outdo their counterparts on the right is calls to violence. They're even willing to pay students if they will target biomedical students who use animals in research. Check this out:
Now university campuses, especially public ones, are havens for advocates and activists for all sorts of causes, and that’s as it should be. Educational institutions should be arenas for dissenting opinions and points of view. Most certainly are.The thugs are coming - Ohio State research blog
But as open as these parts of society are, there are limits on causes celebres and on what their proponents can do. And some animal rights activists, because of their violent actions and those of their peers, have lost their right to rebel, at least in the eyes of the majority of the public. Moreover, law enforcement has, in recent years, determined that some in the animal rights movement qualify as domestic terrorists and should be treated appropriately.