If we didn't have a government - say tomorrow there was a complete government collapse and only corporations and people remained - do you genuinely think there would be no one arresting people? Do you think that walmart or disney or whoever would just let people steal from them? No, they would expand their security forces immediately, with no laws to stop them, no laws to say that they can't just kill theives or people who might be theives or employees who try to quit, etc etc. No laws to say they can't just reintroduce child labour or bulldose your house to make a parking lot. How is anyone going to fight them, when the rich have billions to raise an army with whereas normal people have comparatively nothing? It wasn't always the police arresting or killing union people, it was pinkertons or other hired thugs.

unregulated ancap bullshit becomes a land of warlords very quickly.