You can argue that this time we can make communism work guys and abolishing most private property would be considered far left. I don't think violence is implicit in the extreme left like it is with the far right its just the natural consequences of any authoritarian government regardless of orientation.

The other problem with comparing the two is that even though left and right—by American standards— are SOMEWHAT equally represented the far right is like 30% of the pop and the far left more like 1%. Electing the left caries no risk of the extreme folks running the show they barely have a voice. Electing the right implicitly means letting the extremists run the show they are the majority of the right.