The rule that illegally obtained evidence is inadmissible exists to disincentivize the police from obtaining evidence illegally.
But if the police believed, in good faith, that a particular search was legal and reasonable, based on the fact that a judge authorized them to perform it, then excluding the resulting evidence doesn't serve that purpose.
Update: This is not a new thing. The good-faith exception has been in U.S. law for decades. See https://en.wikipedia.org/wiki/Good-faith_exception . You may not like it, but it's not something the judge just made up out of thin air.
But if the police believed, in good faith, that a particular search was legal and reasonable, based on the fact that a judge authorized them to perform it, then excluding the resulting evidence doesn't serve that purpose.
Update: This is not a new thing. The good-faith exception has been in U.S. law for decades. See https://en.wikipedia.org/wiki/Good-faith_exception . You may not like it, but it's not something the judge just made up out of thin air.