I say this only because things like communism and all their promises can only really come about through a revolution and the price in blood is jaw dropping. So much killing. It also almost certainly means people materially worse off for a long time if not the rest of their lives in the wake of this revolution even if over generations it manages to eventually deliver.

These same arguments can be used to ward off a revolution against a dictatorship or absolutist monarchy, though. Or even against slavery.