PEOPLE who assert First Amendment rights usually have something to say. People who assert Fourth and Fifth Amendment rights often have something to hide. That's why many Americans are indifferent, if not downright hostile, to the constitutional rights against unreasonable search and seizure and against self-incrimination.When a defendant beats the rap on what some critics disdainfully call a "technicality," most often the accused has succeeded in getting a piece of evidence or a confession excluded from consideration by the jury. (Or, after the fact, an appeals court throws out a conviction on the ground that the damaging evidence or confession was wrongly presented to the jury.) The evidence or confession is excluded because it was improperly obtained by the police, in violation of the Fourth or Fifth Amendment. That's not a technicality; that's fundamental fairness. The true technicality is the fact that the rights typically are asserted only by people who, but for the rights, would likely be convicted of a crime. So the rights are regarded by many as "criminals' rights." Yet the Fourth and Fifth Amendments are precious shields for all of us. Criminal defendants who claim them, though acting from self-interest, really are claiming them as proxies for every member of society. The much-maligned "exclusionary rule" is a harsh but effective deterrent against police overzealousness. The cop who loses an arrest because he ransacked a drug dealer's house or tapped a mobster's phone without a search warrant based on "probable cause" is less likely to burst into your house or tap your phone on a flimsy hunch. The prosecutor who loses a conviction because a confession was extracted by intimidation is less likely to bully the honest person who, by some mistake, is called before a grand jury. The Rehnquist Supreme Court has been chipping pieces off the safeguards built on the Fourth and Fifth Amendments - as in decisions last term allowing drug-enforcement officers to randomly search bus passengers' luggage after obtaining dubious "consent," and allowing the introduction of some coerced confessions as "harmless error." These are worrisome trends, with conceivable costs to a decent and civil society that far outweigh any marginal benefits to law enforcement.