The argument is that P(customer wants to run their own firmware) cancels out and 2,3 are just the raw probability of you on the receiving end of an evil maid attack. If you think this is a high probability, a locked bootloader won’t save you.
replyVery neat, but 1) is not really P(customer wants to run their own firmware), but P(customer wants to run their own firmware on their own device).
replySo, the first term in 1) and 2) are NOT the same, and it is quite conceivable that the probability of 2) is indeed higher than the one in 1) (which your pseudo-statistical argument aimed to refute, unsuccessfully).