Included in Marx's greatest hits are
"The most capitalist countries will be the first to fall to communism" when in reality the only two major countries to fall to communism were theocratic monarchies that it would be a struggle to call capitalist.
"After the dictatorship of the proletariat the organs of the state will naturally fade away." Yet everytime the proletariat gets into power it seems that the organs of the state only strengthen.
"I shouldn't have to work other people should pay for me to continue to live." It turns out Karl never had a job, and spent most of his life mooching off of others, exactly as he accused the capitalists of doing.
In fact everything Marx said that could be evaluated against reality turned out to be wrong, so why should I trust the rest of what he said?