You're looking at it the wrong way. You're saying that it's impractical to have perfect knowledge of everything the device is doing, but in fact that's not nece

You're looking at it the wrong way. You're saying that it's impractical to have perfect knowledge of everything the device is doing, but in fact that's not necessary. All it would take is to have laws that make it illegal to inspect data in a user's computer except by confiscating the device with a warrant. That would remove all incentive for LEO and companies acting on their behalf to pull stunts like these. It would also mean they would have to have very good tracking to prevent tainting of evidence (since it would otherwise be difficult to tell where a piece of data came from). Obviously this would not secure you from all attackers (e.g. imagine you want to keep some trade secrets, secret), but nothing other than good infosec would. The problem is that a lot of people don't understand why privacy is important and why compromising it for what seems like good reasons is dangerous. Such people don't understand that some laws that make it easier to get away with crimes can still be good.