Che Guevara
In Guevara's private writings from this time (since released), he displays his growing criticism of the Soviet political economy, believing that the Soviets had "forgotten Marx". This led Guevara to denounce a range of Soviet practices including what he saw as their attempt to "air-brush the inherent violence of class struggle integral to the transition from capitalism to socialism", their "dangerous" policy of peaceful co-existence with the United States, their failure to push for a "change in consciousness" towards the idea of work, and their attempt to "liberalize" the socialist economy. Guevara wanted the complete elimination of money, interest, commodity production, the market economy, and "mercantile relationships": all conditions that the Soviets argued would only disappear when world communism was achieved. Disagreeing with this incrementalist approach, Guevara criticized the "Soviet Manual of Political Economy", correctly predicting that if USSR did not abolish the law of value (as Guevara desired), it would eventually return to capitalism.
David Orton (deep ecology)
Che Guevara was no coffee-house revolutionary. He could not be classified as an academic Marxist. Many of these gentlemen—who may be spotted on university campuses in America and Canada, well salaried, well fed and well clothed—make absolute distinctions between revolutionary theory and revolutionary action...Che had an interest in revolutionary theory but he also believed in praxis. His message was brutally simple, yet profound: The revolution will be made by those who act, not by those who endlessly talk and contribute to left-wing journals, regarding strategy, tactics, objective versus subjective conditions, etc, etc.