I always despite this question so much; mainly because everything is a cause of something and a symptom of something at the same time; there is nothing isolated in this world. So you have to give a lot of context to see if -in that context- it is a cause or an effect.

I'm this particular case you could say stupidity is the root cause, but saying so it's too abstract to be usefu/actionable.

It's basically a symptom of a highly imperfect system, where few participants actually have the incentive of seeing justice done.