Corollary: Nobody looks at themselves as malicious. If you think the root cause of a conflict is maliciousness, then you'll think it's someone else's maliciousness. If you think the root cause of a conflict is incompetence, then maybe you'll acknowledge that it could be your incompetence. That may still be difficult, but it's a sign of wisdom.
See also DefendAgainstParanoia, where paranoids assume maliciousness on the part of people who otherwise are indifferent, stupid, or ignorant.
While malice must be fought, stupidity, incompetence and ignorance must be educated. Never flame when you could just point to the manual. However, stupidity does not excuse the real negative repercussions of ignorance: the onus is on those making decisions to be careful and informed. Some people are ignorant by design, and cannot be educated. See Wiki:OnlySayThingsThatCanBeHeard.
For example, prioritising profits over the environment can lead to destruction of virgin forests and pollution of rivers. This may be incompetence rather than malice, if the company is not aware of the negative effects of their actions. No one sets out to pollute the environment as their GoalStatement. However, this shouldn't stop people from attempting to forcibly re-educate the company concerned, or in trying to stop them from causing further damage.
Trying to AssumeStupidityNotMalice is weaker than trying to AssumeGoodFaith. Thus it works as a useful fallback position when the PrincipleOfFirstTrust is violated. Equally, it works as a useful intermediate position when trying to convince a CryptoNaut or anarcho-capitalist to adopt a more charitable view of human nature.
See also WikiPedia:Hanlon's_Razor