The answer is political ideology... study history, “religion” only becomes deadly when it morphs into political ideology. One that demands (like Marxism, Fascism, Islam) your compliance at the point of the sword. Preachers that warn of Hell, cannot act to enforce it on you without an accompanying political ideology to make it happen. In the middle ages the punishments of the Inquisition were executed by the civil (political) authorities. #ThinkAboutIt!
What is most dangerous is theocracy, where both are involved.
I separate “power” from “dangerous” because I see them as different things. Christianity is powerful, but not dangerous.
Japan deified their leader and it led to suicide attacks. Islam leads to suicide attacks. Hitler’s Germany and the Soviets did not have that kind of power over the individual.
And for me, it is, at the end of the day, all about the individual.