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.

Excluding the evidence would incentivize police to stop choosing the most convenient interpretation of the law. They should have to try to make the most accurate interpretation, which means punishment when they are wrong. Just like for everyone else

If I believe, in good faith, I have not broken the law. I should not be convicted.

Agreed. Part of the problem here is that there are few consequences (other than perhaps non-promotion) for judges who issue bad warrants, and we don't have good information on how many warrant applications are rejected or wrongly granted.

It is an established principle. But it also is an exception to how our legal system works: you are usually bound, retroactively, by new legal principles when courts “discover” them.

Reminds me of the de-facto good-faith exemptions for US police for not shooting civilians, or for the US government for arming death squads, or dictators, or genocidal military campaigns etc.

Horseshit. This isn't a criminal conviction, the standard of mens rea doesn't and shouldn't apply. To add a good faith loophole only incentivizes two things: purposeful ignorance and lying.