To be fair they can be retards, wrong in most of what they say, and still be on the right side of history. Right or wrong is independent of history, though. Good guys can lose and bad guys can win. Suggesting there actually is a right side to history is a progressive conceit which assumes a Hegelian metaphysics governs time. I've seen little evidence to support that and the evidence that exists is generally contrary to the policy preferences of the left.