"So you have millions of tiny governing bodies with their own rules and limitations and checkpoints every few blocks, wherein you agree to these contracts."

Yes. It's called poly-centric law.

"Fall on hard times and can't afford to walk on the privatized sidewalk? Too bad."

The sidewalk fee would be negligible. Anyone, even a homeless person, could afford it.

"Sorry your employer exposed you to asbestos without your knowledge, then the cancer made you lose said job since your employer refused to help pay for insurance. Or maybe they promised to help when you started working there, and then decided not to when push came to shove. Oh well, better luck at the next employer. Let's say you find enough kind people to let you walk on their sidewalks for free, and you find a job. 2 weeks in, you expect a paycheck. They decide not to pay. Oops, you should have worked harder, or known better, or been born someone else. All your fault, all your problem!"

You are free to sue them in a poly-centric court and if there was any paper document or contract you'd likely win. A lot of money. More than likely, though, a company wouldn't want to practice these acts as it is bad business. They would get a shit reputation and smart, decent people would not patronize them. No worker in their right mind would take a job there after news hit as well, and they'd never be able to retain any talent.

"You try to rally support from other workers who got fucked over, but the ones who tried to enact change were executed. The community leaders who tried to do the same met the same fate. With no governing body to remove these people from society, they're free to do as they please. As long as they pay their protectors enough, they're safe."

Once again. This is bad business, so more than likely they wouldn't want to engage in this practice as it is stupid for profit-making. Second, if they did murder is still abhorrent and a social stigma even in Ancapistan. If they killed their workers, people from their own community would not tolerate it and banish them. Most people in Ancapistan would have their own weapons, so good luck to that company. It's a possibility, I suppose, but not very likely. I will keep this in mind.

"No job, ill, and destitute you find an alley to collapse in and find some rest. Oops, you got picked up by the building owner. His rules said you couldn't sleep there, and by sleeping there, you end up in a prison camp. The rules weren't posted anywhere, but you're responsible for knowing them anyway. At least now you get to eat once a day, right?"

If the rules weren't evident for interested parties, then they would have no right to enforce their property rights. They could throw in a private prison, but you'd likely sue and win. All of this is negated as no business would let it get to this as THERE IS NO PROFIT MOTIVE HERE AND THEY WOULD WASTE CAPITAL.

But seriously. This is good fodder for a meetup, don'tcha think?