It's about owning your hardware, not safety. A person that's willing to go through the hassle knows the consequences of such actions and how to deal with them.
Do "normal people" need to do that? Absolutely not. Should it be easy to do that? Absolutely not. But for those of us that really want to own our hardware, there should be a way of doing so without relying on exploits.
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.