Stefan Molyneux claimed that many people who back Marxism are stupid, that they simply don't realise the logical fallacies and other problems in Marxist "thought". I believe that this is not the best explanation for Marx's popularity. I think that practically all supporters of Marxist thought are capable of understanding the gross flaws in it but choose not to do so. These two hypothesis predict significantly different results in the real world, so they are not simply academic or arbitrary differences, but distinct and testable.
If people were really accepting Marxism from stupidity then when an idea that was too stupid to accept came along, they would not accept it. If on the other hand they were not, they would accept it, if doing so achieved the same goals as accepting Marxism. I have found such a stupid idea, the 12:1 law. This law said that a company could not pay anyone more than 12 times what it paid it's lowest paid employee. I'm still not clear on whether that meant per year, per hour, per week, or what. It doesn't matter.
To show that this law was not supported out of stupidity think really quickly; what are the first two consequences of this law to come to mind. Unless your mind works really oddly it will be "some people will get pay raises and some people will get pay cuts.". Now ask yourself, did these people do anything to deserve either? No.
It's blatantly obvious that some workers will get no pay raise since the company either does, or will pay it's CEO less than 12 times their income. Others on exactly the same pay will get a raise, despite doing the same work under the same conditions, just for another company. That is clearly unfair. If someone had wanted to benefit workers they could simply have lobbied for more union power, a higher minimum wage, lower taxes on the "poor" and more on the rich etc. But they didn't. They choose to back this idea. It is impossible to believe that those who voted for the law didn't figure out, and had no friends that figured out, that the effect would to hugely unfair to some workers. Even people who are extremely stupid must at some point mention their stupidity to smart people, who will correct them. But apparently for a significant proportion of the Swiss population that didn't happen. Which suggests that it's not stupidity, but deliberate avoidance of the facts. Rand said the only evil thought was the refusal to think, and this is a prime example.