Don’tcha just think brainwashing is a more realistic answer?
Brainwashing has its limitations. Unless it is constantly reinforced, it tends to degenerate.
What stands out about liberalism-leftism are several very clinical behaviors. First of all, they tend to share very similar irrational ideas, something which is seen in other clinical mental illness, such as the tin foil hat wearers. Why do they all do it the same way? It implies a similar, organic reason.
Second, they can neither be persuaded of the irrationality of their ideas, nor can repeated demonstration of those ideas failing dissuade them. No sense of pattern recognition.
Third, a whole slew of their ideas seem to be self-destructive in nature. They despise safe and noble behavior and encourage high risk, dangerous and even murderous behavior. Their friends are treated as enemies, and their enemies as friends. They are deeply critical of important elements to their lives, like energy, self defense, and healthy social behavior.
In other words, like they are on a path to destruction, and want to take as many with them as they can. Just like a rat attracted to the smell of cat urine.