Marxists at least understand how capitalism works—those who don't own capital work for those who do; they just characterize it as being zero-sum (employer benefits, labor doesn't) when it isn't. It used to be damn close to zero-sum, that was why Marxism actually looked good in the first place, but it's not the 19th century anymore.
But have you really seen any evidence that our "progressives" have any knowledge of that theory? Ask any of them how capitalism works. Will you really get "investor class, dispossessed proletariat"? No, you'll get sob stories and slogans. Marxism may have been a wrongheaded theory, but it was one; our left don't have a theory, they have mythology.