It's not just about punishing the cops, though. The problem is that illegal searches are Fourth Amendment violations -- which we take very seriously -- and this

It's not just about punishing the cops, though. The problem is that illegal searches are Fourth Amendment violations -- which we take very seriously -- and this seems to be the best way of preventing them. Usually constitutional violations are handled in a compensatory manner, but it probably wouldn't work to rely on lawsuits for 4th Amendment violations. How much to compensate for a police officer illegally searching your backpack? Probably a nominal amount, and certainly not enough to prevent police from committing illegal searches in the future -- it would just be considered part of the cost of securing a conviction, and illegal searches would be rampant. And it's hard to imagine the victims of most of these illegal searches being able to find lawyers to take the cases (not worth it). Excluding illegally obtained evidence (the "exclusionary rule") is the best way we've come up with to consistently protect these rights. The obvious downside is that we throw out tons of perfectly good evidence and lose lots of convictions, which is why the rule seems absurd to many people, especially lawyers from other countries. But we're essentially forced by the constitution to consider illegal searches a more serious evil than a missed conviction.