That's also just propaganda. When we're taught random stuff, like philosophy, we don't necessarily jump off to a negative conclusion. It's mostly with political stuff where we're beaten down to think that things like redistribution or socialism is "good in theory but bad in practice", that "humans are selfish by nature", that "anyone with power is corrupted so we shouldn't aim to have it", and so on, so by the time you encounter leftist theory you don't treat it with the same grace you would if you read, say, Aristotle, but as a reflection of poor character ("they must have had a secret agenda of domination!"), or poor understanding ("did Marx never hear about human nature? what a dumbass!") or both. When we actually open up to the idea that people like Marx and Engels and others could be right, and read it with an open mind, we can very easily work out that they were right.