It seems like the discussion would need to be... what information that law enforcement wants to have classified as "limited" which the public finds acceptable to definitely be hackable by third parties who will inevitably figure out how to bypass the encryption. Even if it's just a corrupt FBI agent selling the key on the black market, all it takes is one time.

There might be some subset of things that fit this. Maybe a call record? But would the public be cool with the Russian Mafia definitely being able to get their GPS location and text message contents? Saved passwords? All your emails from the last decade? That's how I see the tradeoff and risk. There is little that the FBI would be interested in that criminals wouldn't be able to make a buck off of.