The explanation for this (according to Jonathan Haidt) is that early humans developed weapons like spears and axes, which made it easier to kill other humans. So it is relatively easy for a larger, stronger alpha male chimp or ape to dominate weaker males, but a human alpha male bully would often end up getting speared by a lower status rival.
That sounds pretty similar to the argument that high gun ownership makes makes it more difficult for the government to become tyrannical.
What is something you used to believe, preferably something concrete with direct or implied predictions, that you now know was dead wrong. Was your belief rational given what you knew and could know back then, or was it irrational, and why?
Edit: I feel like some of these are getting a bit glib and political. Please try to explain what false assumptions or biases were underlying your beliefs - be introspective - this is LW after all.