Getting evidence would be a challenge if policing were done entirely by private firms with no State granting them special authority over ordinary citizens.<p>For instance, you suspect that I stole something of yours and have it in my house. You hire a private police force to investigate. If they knock on my door and asked me to let them come in and look around, I'll laugh at them and close the door.<p>If they threaten to use force, the different private police force whose services I subscribe to will use force to stop your private police force.<p>Some advocates of entirely private law enforcement/justice systems I've discussed this with tell me that this won't be a problem because my neighbors will see that I'm not letting your private police force in, and that will tarnish my reputation. Reputation will be very important in a government free society, they say, and so I will not risk that unless I'm guilty.<p>I don't buy that...I think it is far more likely that most of my neighbors would be thinking I'm doing exactly what they would do if some jerk accused them of stealing and wanted them to let some private police force come in--worse, a private police force that has been hired by their accuser and so has a strong incentive to please him. They want him to give them a good review, so more people will hire them.<p>Some have told me that your private police force could get a search warrant from a private court. That just pushes the problem back one level, for unless there is some State forcing me to recognize the authority of your private court, I will no more recognize your court than I recognize your police force.<p>Every way I've thought of, or heard anyone propose, to make this actually works ends up in effect recreating a State under a different name.