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Stupidity is the worst form of evil.
Stupidity is a more dangerous enemy of the good than malice.
You can probably find the above quote from different places. There are plenty of materials and philosophy on the subject matter. Dietrich Bonhoeffer may be the more modern one. But some can be traced back to ancient Greek.
As with everything philosophy, there isn't always a concrete, scientific, right or wrong answer. And different age group, which related to different stage of life in experience may also have different answers. The word of stupidity and evil or malice may also have subtle difference depending on context which makes discussions of the subject matter even more difficult.
Stupid can be evil, though. But still, it needs a planing capacity of the stupid brain.
For example, stupid switches off the electricity of a local hospital as revenge for firing him. Done a stupid thing. It's evil because a lot of people could get problems.
Vs.
Evil gets fired and make an evil plan to destroy his ex employer. After weeks of planning, the electricity had been switched off.
That's my logical and philosophical approach.