The Supreme Court has recently watered down the exclusionary rule in a decision that has affirmed a conviction even where there was a bad warrant and faulty arrest. Now evidence obtained through negligence will be admissable, meaning that police have less reason to be careful in their investigations, searches and arrests.
The exclusionary rule is not included explicitly in the Fourth Amendment, but it is one of the few ways the amendment has any teeth. If there are no consequences for prosecution when police trample on our rights to be free from unreasonable search and seizure, police can be expected to face less pressure from district attorneys to obey Constitutional limits on their searches.
It might offend our sense of justice to see criminals get away, despite clear proof of their guilt, simply because of a police error. But this is true not only of negligent searches but ones where the police break down doors knowing full well they have no legal right to. The exclusionary rule is an important check on the abuse of state power, and although it lets the occasional guilty party off, it has given the innocent a deal of protection from arbitrary violations of their privacy. Ideally, guilt or innocence would be all that matters, but in the real world, we need checks and balances in the criminal justice system just as we do in the relations among the different branches of government.
Furthermore, many if not most criminal justice activity is conducted over victimless crimes such as drug offenses. Programs like the drug war, where there are no victims to complain and testify about the crime, are very difficult to implement when full constitutional civil liberties are honored. Thus, those who want to erect a police state and carry out such crusades against such offenses need to favor erosions of the Bill of Rights just to see their program work anywhere nearly as well as laws against murder, theft, rape and real crimes against person and property, which are easier to enforce than victimless crime laws in a free society.
For all these reasons, any envervation of the exclusionary rule should be seen in the same light as measures that compromise the other traditional safeguards enjoyed by the defense, such as the trial by jury, freedom from self-incrimination, the right to confront the accuser and so forth. In any of these cases, we might lament that the guilty gets an advantage, but such advantages are necessary to preserve a free society and to protect the rights of the innocent.
This is an unsettling Court decision. While Obama represents an executive, legislative and judicial philosophy quite at odds with liberty, one silver lining of his administration might be new judges who, at least on these issues, are effectively more protective of freedom and civil society than are their conservative counterparts. On the other hand, Eric Holder, while rhetorically better on some important issues like torture than Republicans like Ashcroft, Gonzales and Mukasey, has shown himself to be no friend of the rights of accused as well as of other constitutional rights like the 2nd Amendment, as David Theroux notes below.