Yeah, pointing to the problem is quite easier than figuring out a solution.

As far as I'm concerned, I actually read the popups and having to click okay about five or six times in a row would make me second-guess my decision. Would that work for everyone? Most of the people? Some of the people? I don't know that answer.

> I'm not even sure if such a barrier should be technological or legal.

My answer would be both. I highly doubt it's in hardware manufacturer's interest to figure out a technological solution, but if there's some legal incentive for them to at least try, they'll figure out a technological solution.

Android's option of connecting the device to a computer over USB, running a program on the computer, logging into the device, seeing a scary warning and wiping the device seems to work well. I don't think I've heard of a large number of people being tricked into unlocking their bootloader — at worst, a handful of script kiddies might have been tricked.