It’s more insidious than teaching us to “hate” Marxism. They teach us “oh, it’s lovely in theory but because of that darn human nature that makes all of us so greedy it can never work in practice.”
Saying it's human nature to be greedy while they live in a capitalist society is like saying it's human nature to drown while they are held under water.
I'm not well read in Marxism so I'm probably not qualified to answer this, but the recurring issue with Communism seems to be the same as capitalism, in that it requires people to not be assholes in order to properly function.
The Communist Manifesto was a pamphlet written within the context of Marx's time, and the Material Conditions that came with them. They were not meant to be the solution, but a solution, and for his time period.
Reading the Communist Manifesto as a means to say Marx's ideas are problematic by stripping them from their context and slapping them onto modern times is a disservice to Marxism.
Marxism is a frame of analysis, a philosophical method via Dialectical Materialism, and a tool for looking at how to improve whatever situation you are in. As such, further reading of Marx beyond the Manifesto is a requirement to understand what Marxists of today advocate for.