Tens of thousands of years of human history. Feuding warlords, and slaves, rather than everyone acting together in unity.
> What is a demonstrably false fairy tale is that we don't act righteously when law enforcement is present. So asking what would happen in its absence seems irrelevant.
Well, we don't have mass rape, looting, or murder. One really needs to compare scale. Democracy seems to be a horrible system, and indeed the worst system, except for all the others (paraphrasing Churchill).
> Self-regulating organisations are possible, the only real condition is the removal of external incentives for those organisations to misbehave.
You're missing scale. SMALL self-regulating organizations do very well. The key condition isn't just about removing external incentives, but also about scale.
Once you're at some scale, you're guaranteed to have a few psychopaths who work to game the system to personal benefit. A key thing about small-scale is everyone can say "Adolf is a jerk. Let's swing clear of him." Large scale, he takes over Germany, and onto the world!
Likewise, large-scale, you're missing social incentives. Small scale, I can say "I won't steal from you, because you'll think I'm a jerk." Large-scale, try leaving your wallet in the train in almost any major city for 10 minutes.
Tribal culture was pretty good on isolated islands. It didn't go Lord of the Flies. That only happened at scale.
I've seen largish organizations sustain this for maybe a half-decade or decade, but never longer. At some point, game-theoretical organizational models take over, and things never go back.