Tell your opponent to post again once he's completed his university/college and has a more nuanced understanding of Marxist social theory. His posts read like a 1st or 2nd year sociology student. (I say this as someone who has studied and generally agrees with a fair bit of the Marxist sociological paradigm).
Marx posited that all conflict is born of economics and the disparity between the proletariat (workers) and bourgeouis (owners). He was also writing in the late 19th and early 20th century. He also didn't have much of a human history education, and relied on broad generalizations about the history and past of human civilization. Last, he also didn't live to see the evolution of the middle class, which throws an uncomfortable wrench into traditional Marxist theory.
Marx got a lot of things right (depending on your perspective), but his belief that class conflict underlies all conflict was quite naive, as is your opponent's position. We human beings have both cooperation and conflict behaviours programmed into our very biology; economic conflict is a symptom, not a cause. The fact of the matter is that humans form social groups of varying sizes, and compete with other human social groups for resources (and not necessarily for scarcity, but frequently just because we can; human history is rife with examples of invasions and wars fought for no other reason than the opposing group is different in some way from the in-group). While I sincerely hope that one day this competition and conflict will be expressed in ways other than lethal violence, I really do wonder if we'll ever get there.
Anyway, the fellow you're arguing with is approaching your discussion from a philosophical and ideological standpoint, and isn't heavily relying on facts. If you'd like to knock him down a peg or two, ask him to speak in facts instead of his glorious vision of what would be. His entire premise is based on the assumption that class conflict underlies all conflict, and there is ample historical evidence to thoroughly debunk that notion.
That, and know-it-all first- and second- year university arts students are really, really tedious to listen to.