I believe stop and frisk can be justified. This is certainly true from the anarcho capitalist libertarian point of view. Here, all streets would be in private hands,

Block, Walter E. 2009. The Privatization of Roads and Highways: Human and Economic Factors; Auburn, AL: The Mises Institute; http://www.amazon.com/Privatization-Roads-And-Highways-Factors/dp/1279887303/ref=sr_1_1?s=books&ie=UTF8&qid=1336605800&sr=1-1

and the owners might well employ this policy in order to safeguard their customers.

What about from the minarchist point of view? Here it is more difficult to make this case, but I think it can be done, stipulating that the purpose is not to stop victimless crimes like drug selling, but, rather, crimes with victims such as rape, murder, theft, etc.

Suppose members of gang X are raping a woman, and members of gang Y stop the Xers from so doing. Are the Yers justified in protecting the woman? I claim they are. Are the Yers good guys? No, they are gang members too, and often engage in just such depredations. But, in this single isolated case, if you ignore their other crimes, they are good guys.

A similar analysis applies to government police. From the an cap perspective, they are just another gang. Says Mr. Libertarian on this (Rothbard, 1973, p. 49): “if you wish to know how libertarians regard the State and any of its acts, simply think of the State as a criminal band, and all of the libertarian attitudes will logically fall into place.” Rothbard, Murray N. 1973. For a New Liberty, Macmillan, New York; http://mises.org/rothbard/newlibertywhole.asp

Therefore, the government cops are in the same position as the Y gang is. In this one instance, they are justified. They frisk someone they deem suspicious, he has weapons, he was about to commit a crime, and cannot do so because he is arrested.

Certainly private police may stop and frisk dangerous looking people on the private property they are hired to protect, as in an-cap. That is an easy call.

The Best of Walter E. Block