Good and evil is what the left, in each specific case, decides what it is. There is no consistency in moral relativism. The left didn't "understand the inner child of the depraved and muderous" Slobodan Milosevic. They were unconcerned about Serbian babies and supported the destruction of Slobo's regime, no matter what the cost.
Almost 100% of the time, when the right chooses a position based on moral reasons, the left will choose the opposite position. If Clinton were president and opted to fight this battle (a long shot, to be sure), the left would be applauding his every decision.
IMO, you hit the nail exactly on the head with the above. Socialism, in its effort to make "equal" those who are not equal, must by necessity resort to arbitrary decision making and use of law to achieve their vaunted "egalitarianism."
Our American tradition of individual freedom, OTOH, requires the law be applied equally to all.
So I think that socialism and leftist philosophy, by their very nature, require the world to be seen in shades of gray, while the American tradition, which requires a different kind of equality, equality before the law, requires at least some absolutes.