"Never attribute to malice that which can be adequately explained by stupidity."
"Hanlon's razor is essentially a special case of Occam's razor. Occam's razor states that, assuming equal explanatory power, the simplest solution (formally, the one with fewest assumptions) should be preferred. Assuming intent is a pretty big assumption, but we all know that (other) people are idiots. "
The thing is that Hanlon's Razor ISN'T a special case of Occam's razor. There is no actual evidence given that you need LESS assumptions to believe in stupidity than bad intent as a general principle. Assuming intent isn't a really big assumption in all circumstances, in fact people have intent for all of their actions. We do know that other people are idiots but we also aware that they act badly for their own benefit. In fact we could reverse the rule and say "Never attribute to stupidity that which can be adequately explained by malice.". What does "adequately" mean in this context? Well if it means "in a way that explains all facts better than any competing explanation" then the aphorism is redundant. If it means something else it's simply wrong. The fact that you can give an explanation based on stupidity that somewhat fits the facts isn't convincing if another explanation fits the facts better.
Say for instance we're trying to figure out the reason for a particular disastrous government policy. Suppose that this policy was disastrous for poor working black people but relatively good for white, unionized, relatively well off workers. Either the people who passed it didn't realize that this or they didn't care as long as it benefited white unionized workers. Now Hanlon's Razor would have you believe the former as long as it was an "adequate" explanation. But how would that be determined? Unless we have full details of the IQs, education and training of all the people making the decision how would we know how stupid they're likely to be? It would be one thing if legislation were made only by those who were utterly ignorant, but it's not . We do know that legislation is however made by people who want the support of various groups, including white, unionized workers. So they might well try to gain that support whether or not it was bad for poor blacks. And this leads to another problem with Hanlon's Razor, it assumes stupidity isn't the result of motivation. But we know that how much thought people people put into a subject depends on what they are motivated by. Therefore a policy that harms somebody could well be the result of malice because their interest was ignored in the formation of the policy.