If Silicon Valley were to make a magic backdoor that only opened for the good guys with pure intentions, the government wouldn't be able to access it anyway, so I'm not sure why they're pushing for it.
Why does this make "Sleeping Beauty does Anal" pop into my head?
As far as I'm concerned the standard should be what they could have seen in 1800. In other words, any capabilities from tech newer than the Bill of Rights should be denied to police by default unless they get a warrant. (And banned to private snoops as well.)
The way the law is written today, possession is a felony, period. Intent is not required. If some hacker in Russia thinks it's funny to write a virus that loads child porn on your computer and then calls the cops on you, you're a felon.
If the appeals courts had any humanity at all, they'd change that and require proof of intent for any felony conviction. (And put some teeth in the 8th Amendment, so prosecutors couldn't just force you to confess by threatening you with life-without-parole if you go to trial.) But so far, the Supreme Court continues to have a majority of monsters on it.
The comments on those two WP posts explain it somewhat better.
The kicker is that the court drew an analogy to where an accused person has a locked safe or lockbox that may contain evidence. Existing precedents say that prosecutors may demand you turn over the key -- but they may not demand you turn over the combination if it's a combination lock.
And the password on your phone is more like that combination.