The jury had to kill Socrates because he mistakenly took democracy seriously. He thought that any individual would have to be accountable for the high domain of political rationalization. He thought any schlub in the agora should be able to give an account of truth, justice, nobility, and so on. He refused to route his questions through the appropriate social technologies that Athens' oligarchs had provided to diffuse this accountability: the priests, the mystery cults, etc.