I would note that DHS/CBP can't do too much of this. It's very time-consuming even to set aside a passenger and demand their devices and passwords, and CBP has large plane loads to process quickly. So obviously they must only bother with this policy when they think they have reason to -- because you're on some list, or perhaps because someone with the same name as you is on a list (scary!). There are some natural limits to this policy.