Because all people everywhere are psychopaths who will stab you for $5 if they can get away with it? If you take that attitude, why even go to "work" or run a "business"? It'd be so much more efficient to just stab-stab-stab and take the money directly.
I'll indulge your straw man because it's actually pretty good at illustrating my point. 99.9% of people are not psychopaths. But you only need .1% of people to be psychopaths. In a world where you get $5 and no threat of prosecution for stabbing people, you can bet that there will be extremely efficient and effective stabbing companies run by those psychopaths. Even normal people who don't like stabbing others would see the psychopaths getting rich and think to themselves "well, everyone's getting stabbed anyway, I might as well make some money too". That's what a race to the bottom is.
And that's why the government regulates stabbing.
> Because all people everywhere are psychopaths who will stab you for $5 if they can get away with it?
Not all people everywhere, but most successful businesspeople.
> It'd be so much more efficient to just stab-stab-stab and take the money directly.
It isn't though? If you do that then you get locked up and lose the money, so the smart psychopaths go into business instead.
> It'd be so much more efficient to just stab-stab-stab and take the money directly.
which is exactly what the law of the jungle is. And guess who sits at the top within that regime?
Humans would devolve back into that, if not for the violence enforcement from the state. Therefore, it is the responsibility of the state to make sure regulations are sound to prevent the stab-stab-stab, not the responsibility of the individual to not take advantage of a situation that would have been advantageous to take.