The fundamental problem of the Left is that they cannot deal with reality.
The universe is a chaotic, and inherently "unfair" place, and the Left (like the Arabs), are unable to deal with that reality: so they attempt to anthropomorphize the universe and pin the blame on a human agent. That's how this "oppressor-opressed" model comes into being.
It never occurs to them that in our current world, especially in America, that the rich and powerful don't become that way by "oppressing" others: they become that way by pleasing others. Carnegie, provided bulk transport. Rockefeller, provided oil. Kennedy, provided booze. Michael Jackson, provided biologists a lifetime of research.
Er, you get my point. That doesn't mean that the rich and powerful won't BECOME oppressors, once they have achieved wealth and power: George Soros, Ted Kennedy, some of the Rockefellers, as examples. And most "community organizers."
But these aren't problems of governance, they are problems of human nature. Since they are anathema to the Left (so they say, although most are seduced by power), their solution is to attempt to change the fundamental nature of humanity, a windmill too far if you will. And since they eschew religion, and the associated questions of the source of moral or ethical behavior, they have nowhere to turn to for answers except within: which leads to the fundamental paradox of their outlook~if there is no higher source of morality than themselves, then there is nothing to prevent them from becoming the oppressors they claim to despise.