That’s because the enforcement actions taken by citizens, will lead to interventions, and the expenditure of investigative resources (and possible follow-up prosecution, etc.) by the government. These actions contradict the proposition of neutrality in the matter, and nullify the notional economic savings on the government account.
Consider that the government chooses to consider that robbery of less than twenty dollars, is not an offense that will be prosecuted. Naturally, criminals will take advantage of the opportunity; but at some point, citizens will start to fight back, with the result that the criminal, citizen, or both, seriously is injured or killed. The offense of murder would be investigated with major expenditure of resources by the government, leading to incurred costs (just for the investigation) of tens of thousands of dollars, and then the prosecution of the criminal for murder, and subsequent prison sentence. This contrasts with the costs of a sting operation, which in conclusion, would cost less money for investigation, prosecution, and the length of the prison sentence. Moreover, the deterrence caused by this law enforcement, greatly reduces the number of such offenses, therefore reducing the overall costs.
With that context, let us consider what the proposition of neutrality really could express in this case. What is the range of responses, that the citizen could take, that would not result in punishment by the state?
- Can the citizen rob the robber back?
- How much force can the citizen apply to the robber in response?
- Can the citizen set up a sting operation, or other formalized remediation, and detain the robber?
Only in the case when the citizen robs the robber in return, could the level of force applied remain in the neutral area, and not require a further investigation, including the determination of blame, which then would be the basis for legal actions.
For further clarity: consider the case where the citizen resists the robbery, for example by not handing the robber money. Consider that the citizen fights back with hands and feet against the robber, when the robber lays hands on them to get the money anyway. If you consider that such resistance by the citizen is criminal, then the state has entitled the robber to prey upon the people, and therefore is not taking a neutral position. In this situation of ordinary force, the robber’s use of force remains within the original premise that robbery less than twenty dollars won’t be prosecuted. Hence to remain neutral, the state would have to consider that forcible resistance by the citizen, also would not be criminal.
The end state is that it would be an ordinary occurrence, to see street fighting. Street fighting, in general, likely would lead to serious harms, to which the state would not be neutral. Hence, a police officer would choose to break up the fight. However, how would the police officer determine which is the citizen, and which is the robber, to restore a previous state? Under the policy of neutrality, the status quo at the end of the fight would determine who keeps the money. That is, the most likely scenario is that the police officer would break up the fight once the robber already had taken the money, or done injury to the citizen, leaving the citizen without means to rob the money back, or to injure/deter the robber. Hence, the police officer, on average, would intervene on the side of the robber, and therefore would not be acting neutrally.