A leftist has no enemies to the left, and no friends to the right. Thus everyone that he is a friend to, is an enemy to him, and everyone who is a friend to him, he is an enemy to.
Back in the day of the Soviet Union, we regularly saw this dynamic with the “popular front”. The popular front, a coalition between moderates and radicals, would seemingly be dominated and led by moderate bourgeois, which moderates would be swiftly dumped once the front took over. But not only would the radicals think they had it coming for not being left enough, the moderates themselves seemed to feel they had it coming for not being left enough.
We also saw this dynamic in the Soviet Union during the purges. An influential Soviet officer and/or party member, a long way from Moscow, surrounded by armed people personally loyal to him, would be summoned to Moscow to face torture and death. Instead of looting the armory and fleeing for the hills, off he would dutifully go to Moscow.
And today, we once again see this dynamic in the Tucson murders. Jared Lee Loughner murdered a bunch of leftists. Naturally, many people, myself among them, figured Loughner for a Tea Partier, but it soon became apparent that Loughner was a leftist killing them for insufficient leftism.
And so, naturally and predictably, Loughner was forgiven, but the Tea Party was not. J Eric Fuller, who was shot in the knee by Loughner, announced his forgiveness of Loughner, but threatened to kill Tea Partier Trent Humpries.
Here is a word of advice for any leftists planning to die in blaze of glory killing those who commit themselves insufficiently to the one true faith: Practice on a shooting range first. Get them in the head or torso, not the knee. Remember: torso.