Earlier quoted context omitted.
I hope you're aware that "left wing" doesn't mean "socialist" or "communist" and that plenty of liberal democracies have had social democratic parties in power for some period or another without there being any breakdown in tolerance to opposing viewpoints.
Of course it also means socialists and communists among other leftist parties. They represent the pure leftist ideology from which other leftist parties take ideas from, and the closer to center those parties are the more they tone the communistic ideals down. In essence the tip of the left wing is completely intolerable and illiberal.
Both right and left approach a similar looking set of ideologies at their extremes. I'm arguing that the left runs the risk of being overrun by something that moderate liberal lefties like me should be very concerned about.