Perhaps the centralization of governance and the asymmetric power of government over the people is the problem.

If a village of 20 people found out one of their members had been poisoning them for years, knowingly, to attain status as the mage/technocrat/leader, I suspect their punishment would be severe.

Instead, any one person or small group of people feels powerless against a seemingly infinite bureaucracy and a justice system that would sooner punish "vigilantes" than hold powerful people to account for their malice and damage to society.

You give more agency to the modern individual than I do, I think.