Both the Left and Right have adopted the philosophical foundation of Hegel. The term "modern" actually refers to a slate of crazy theories that became popular in the early 1800s. Hegel's modern logic is a system with paradox at the foundation of reason and conflict at the surface.
This form of reactionary thinking started on the right and was picked up on the left. I've written a slew post showing the Hegelian influence in right wing groups.
I find that Eric Fromm's work "Marx's Concept of Man" does a good job of showing how this Hegelian world view became entrenched on the Left.
Rightwing thinkers like to position Marx as an enemy of liberty and themselves as the staunch defender of liberty. The more complex truth is that both the right and left have developed paradoxical definitions of liberty. They then use their paradoxes to create a political climate that benefits their friends and punishes their enemies. This quote from Mr. Fromm's preface encapsulates the Marxian feel towards liberty.
"Marx's philosophy is one of protest; it is a protest imbued with faith in man, in his capacity to liberate himself, and to realize his potentials."
The Left believes that freedom comes through the act of revolution. Leftists target people as their enemy, they then launch into a shrill never ending protest (revolution) against their enemies.
In the bizarre Marxian world view, man is by nature a pile of contradictions. The revolutionary exploits these contradictions. Leftists will do things like label a group as "oppressor" then launch into a campaign to oppress the group (naively failing to recognize that they are now the oppressor). Leftist community organizers will unite half a community against the other half in their grub for power, failing to realize that they are the source of the division.
My favorite example of Marxian Nonsense is the historical fact that Marx is the father of Modern Capitalism. Marx spent the bulk of his career penning the multi-tome work called "Das Kapital" which lays the logical foundation for the economic foundation that they rail against.
The great historical irony is that right-wingers have taken to defending Marx's view of Capitalism rather than defending the Classical Liberal Concept of a free market.
Personally, I think "Marx's Concept of Man" does a better job of explaining the paradoxical foundations of Marx's thought than either "Das Kapital" or Marx's "Manifesto." "Das Kapital" was written to define and project negative images on to "Capitalism."
I cannot repeat enough: Karl Marx is the father of Modern Capitalism. Capitalism as practiced on Wall Street is from a dark fantasy written by a person who wanted to destroy the free market.
The Manifesto was written to raise people in rebellion against the strawman that Marx created in Das Kapital.
In "Marx's Concept of Man," Eric Fromm presents some of Marx's philosophical writings which help expose why Marx took this divisive approach to economics. To repeat: Das Kapital creates a strawman. The Manifesto raises people in revolution against the strawman. Neither of these works explains why a person would do such a hateful thing.
Marx's Concept of Man shows Marx's paradoxical view of mankind and his naive notion that revolution would release man's potential.