In order to win a Section 1983 lawsuit against a police officer, the plaintiff must show, first that a police officer violated the law; and second, that the law was clearly established at the time of the violation. If the law was not clearly established at the time of the rights violation, the officer is entitled to qualified immunity from suit, i.e., he skates.
In Los Angeles County v. Rettele, a per curiam Court held that it was not unreasonable under the Fourth Amendment for police officers to order a naked couple to remain standing with everything showing. While I think that ruling was a bad one, Justice John Paul Stevens proposed an even worse rule:
[No case] clearly establish the unconstitutionality of the officers’ conduct. Consequently, regardless of the proper answer to the constitutional question, the defendants were entitled to qualified immunity. I ... disavow the unwise practice of deciding constitutional questions in advance of the necessity for doing so.
Slip op. at 9 (emphasis added). Imagine if Justice Stevens' rule were widely applied. That is, in every tough case courts would hold, "We won't say whether what the officers did here was a constitutional rights violation. What we will say is that, even if it was, the law was not clearly established at the time of the officer's conduct." How could the law ever get clearly established in such a world?
Isn't it better to have more clarity in the law? (Steve Minor has similar thoughts here.) Wouldn't it be better for officers to know in advance what they can or can't do? Indeed, isn't it fundamental to the rule of law that all laws be knowable in advance?
Surely Justice Stevens would not contend that the Rettelle's Court's deciding the constitutional question amounted to an advisory opinion. There was a live case or controversy before the Court, namely, litigants sued claiming it was unreasonable to hold them naked at gunpoint. The Court simply said, "Nope, your rights were not violated." Why clarifying the law is an "unwise practice" is beyond me.