They know. They just can’t (or won’t) ever admit it. Leftists are really, really strange that way. I used to try and reason with some of them, at the least the reasonable ones. They are curiously immune to facts, logic, and reason. You can patiently guide them through basic concepts, irrefutable historical examples, lesser known suppressed incidents, science, more historical examples, doesn’t matter.
You’ll part thinking you’ve made a new convert. Then see them again in 6 months and they are even worse! It’s like they just see things the way they wish things would be, and then exclude any information that doesn’t comport with their fantasies, and then make up stuff to try and fortify their fairy tales. Start with a conclusion and work backwards and try to make it fit.
They can’t admit to ever being wrong about anything, or change their worldview, have seen this over and over. It would crush them, they are weak people. It’s easier to fool people than to get them to ever admit they were fooled.
Unfortunately, we live in a deep blue state. My brother and sisters are younger than I am and were more heavily influenced by the media, school, and their friends. They are all liberals and it is exactly as you describe. I often think that I have made some progress with them, but they keep getting worse and worse.