> So what does that leave? It leaves compelling the owner of the phone to unlock it.

You're constructing a false dichotomy. Backdooring all encryption and compelling the accused to provide a password are not the only alternatives. And they're both terrible.

You seem to understand why backdoors are problematic.

If we require the government to prove the original crime in order to convict for refusing to testify then there is no point in making refusal to testify a crime, because any time they could prosecute for it they could already prove the original crime and don't need the testimony. The only way it helps the government is if they are also allowed to convict people who refuse to testify when being prosecuted for crimes they did not commit.

You might argue that an innocent person can be vindicated by telling the truth instead of refusing to testify, so innocent people don't need to refuse to testify. But that doesn't work when the government is playing "show me the man and I'll show you the crime." Everything you say can and will be used against you in a court of law and lying to the police is illegal. You have to be allowed to shut up or the government would be able to convict anyone they want just by compelling them to keep talking until the imperfect human in the fish bowl says something a court will accept as incriminating evidence.

So you want to make an exception for passwords. But if passwords are different than other testimony it's because we should be more protective of them. They're the ultimate fishing expedition. There is no relationship between the password and the crime. If there is no evidence of the crime under investigation whatsoever (perhaps because you didn't do it), they still get to see everything on your phone. Then they can charge you with whatever completely unrelated crime their fishing expedition uncovered and use parallel construction to bypass any restrictions on what the original evidence was supposed to be used for.

Moreover, it remains possible to investigate crimes even if you can't look at the contents of every suspect's device. You still have all the evidence supplied by the victim and witnesses and all the methods of traditional police work that existed before everyone started carrying around personal surveillance devices. Being able to force suspects to supply their passwords might help, but lots of things might help, and most of those things might help enough that it would at least slightly increase the percentage of guilty people convicted. That only tells you that some civil rights come at the cost of not convicting some guilty people. It doesn't imply that we should erase every one that does.

Roper: So now you'd give the Devil benefit of law!

More: Yes. What would you do? Cut a great road through the law to get after the Devil?

Roper: I'd cut down every law in England to do that!

More: Oh? And when the last law was down, and the Devil turned round on you — where would you hide, Roper, the laws all being flat? This country's planted thick with laws from coast to coast — man's laws, not God's — and if you cut them down — and you're just the man to do it — d'you really think you could stand upright in the winds that would blow then? Yes, I'd give the Devil benefit of law, for my own safety's sake.