One might ask: where does this leave the Third Great Cause of Wrongdoing, i.e. insanity?
My brief answer is: leave that to the Bolsheviks. It is a cliche of Communist propaganda that anyone who disagrees with the progressive viewpoint is "insane". (They could also call you "reactionary" but that is tautological, and to me it is a compliment anyway.)
So what exactly is so implausible about the idea of collective insanity, of "Emperor's New Clothes" connivance, of an elite so drunk on ideological purity they can only be considered insane by anyone with real-world experience? It's not that these concepts are implausible, only that they are an unacceptable expansion of the term "insanity", and that they risk releasing Bolsheviks (and crypto- and neo-Bolsheviks) from culpability.
If someone isn't confined to a mental institution, or under house arrest or something analogous, we have no business calling them insane. It is difficult to get out of the habit of using this expression. I've tried. Just because I can envision rightist discipline doesn't mean that I myself am disciplined. Bad habits notwithstanding, I firmly believe that treating personalities as diseases is modernist degeneracy.
This doesn't mean were left to a simple dichotomy to explain wrongdoing. Between wickedness and idiocy lies a variety of conditions like laziness and insincerity. Typically, leftists believe what they believe because they foolishly channel all of their brainpower into the exclusive analysis of Cool Thinking. They've all read The Mismeasure of Man (and believe me, you can quote Gould chapter and verse all you want - if you don't agree with him, the leftists will simply never believe you have read him; a fair number of them haven't read him themselves, and so will not recognize your quotations). Willful ignorance is a form of wickedness, particularly if it is intended to protect the ignorant from cognitive dissonance*. Ignoring all Uncool Thinkers leaves you with no possible way to explain, for example, why black anger has gotten so much worse since the civil rights movement achieved its goals.
Thus you can see that leftism is not a product of insanity at all, but selfishness and immaturity. A grown-up will note when a government program has the opposite of its intended effect, and will be willing to note that aloud even if he can't do anything about it. Pilloried for criticizing "progress", the grown-up may be forced by economic or political considerations to keep his mouth shut, but he's not going to adjust his thinking so he doesn't have to carry the "burden" of believing mass opinion to be wrong.
The ethical, mature individual uses the full force of his mind to analyze government policies, even if that means being Uncool. Many wicked, sane people have developed ways to combat this.
* Let's not confuse cognitive dissonance with doublethink.