About 300,000 years ago, when the first humans were born.
The problems being described in this post are the result of the greed of the wealthy, and that has been menacing humanity for as long as there's been humanity.
Not at all. For the vast majority of our time as a species we lived in small hunting and gathering bands wherein the accumulation of personal wealth and property wasn't really possible and one's status instead depended on merit. It's only with the dawn of agriculture, about 10k years ago, that the accumulation of personal wealth and private property becomes a thing. For better or worse, for reasons I don't have the time to go into here, agriculture is a kind of ratcheting trap, and once we embraced it we could never go back and never will.
The thing now is to recreate the small-scale egalitarianism that we evolved to live in, but how we do that in the material world we've created is far beyond me.
No, we don't see any evidence of this at all in the ethnographic literature. To the contrary, what we tend to see is antisocial actors being socially ostracized or killed by the larger group. This is evidently a very old behavior since we absolutely see it in chimp bands as well which means that it goes all the way back to our most recent common ancestor which existed 6 million years ago.
Generally, no. Hierarchy is not the natural order, it's an ideological virus that has been shoved down our throats.
No human is so strong they can face a group, and everyone can be killed with a knife while they sleep. The group can kick someone out or even kill them, but the leader can't just go around like a dictator (if they even had a leader, generally power was not in the hands of just one person). A tribe is like an extended family, you'd have a lifelong personal relationship with everyone - you'd have to be a real asshole to even have to worry about that
Bad stuff happened obviously, but generally people lived like animals - they had territory and would fight other groups over it, but people didn't live in fear and chaos
It takes agriculture and specialization to do the truly terrible stuff. If you don't have people dedicated to being soldiers or guards, you can't wage war (bloodfeuds just aren't in the same ballpark) or impose your will by force. If you don't have agriculture, you don't have much stuff, so it's probably not worth raiding you.
And yeah, people might be stolen or enslaved, but generally there's a path to integration - again, no dedicated guards, so how long can they really keep you in line through force before it gets old?
Then what's stopping post-agricultural people from being disloyal to the rich and killing them in their sleep? What makes you think the same tactics could not be used by pre-agriculture tribal chiefs to ensure loyalty among the tribesmen they abused?
How is that going to work when you live in a group of around 30 to 50 people, all of whom are closely related either through blood or marriage, and all of whom have known you for your entire life?
What we see in all of the ethnographic literature on small-scale hunting and gathering societies is that you absolutely cannot rise to a position of power and influence simply on the basis of strength. To the contrary, the way you gain power and influence is by being a good and wise and generous provider for the group, not by beating your fellow tribe-mates down.
If you know of an example that demonstrates your idea, please do tell, since I am unaware of any such case in the existing anthropological literature.