Re: governments can always legislate
"Then in the UK, we have RIPA that permits TPTB to demand passwords and keys. A suspect in a murder case has just been jailed for failing to divulge his Facebook password under those powers."
And there you have the problem; what if you actually don't know the password and you don't have a way of getting it? An example could be if you create an encrypted file or directory and then don't use it, so you never learn the password and there's no mechanism to recover it; the police could insist you decrypt it (in case it contains something incriminating) but you actually can't remember. Should you go to jail for life?
Could you also end up in jail if someone else places an encrypted file on one of your devices?