Don't forget the dose of radiation for millions of travelers from those scanners. 20 years later thousands of people die of cancer and fucking idiots can't explain why.
https://www.sciencedirect.com/science/article/pii/S168785071...
This is not a what-about-ism, because the very act of flying (which is what border security policies are strictly related to) causes "more harm" in this specific context than the policy itself.
The harm caused by flying itself is also incredibly insignificant, but if someone is going to argue that scanner's radiation is the reason people are getting sick then they must agree that the radiation from the act of flying itself is a much larger issue (and discussing scanner radiation would make no significant difference to whatever harm they think the radiation is doing).
You are describing someone who travels on a plane four days a week, every week, and never takes vacation days. This person also must be checked using the full-body scanner on every single one of their trips (because the magnetic walk-through arches don't use x-rays and thus doesn't have any radiation to speak of -- they use magnets). I think it is more than fair to say that your example is ludicrously cherry-picked -- even if enough people traveled that often to be important enough to bring up in this discussion (the only example I can think of is airplane staff and crew) they almost certainly would not go through a full-body scanner every time they fly.
There was also a study in 2013[1] (which tested the actual scanners in LAX rather than some mocked up scanners), and it claims that a full-body scan only imparts ~11 nSv -- which is almost two orders of magnitude smaller than your ~0.9 μSv figure. I'm not sure which is correct, but I do have a source for my figure.
[1]: https://www.sciencedaily.com/releases/2013/06/130627151642.h...
Which is practically a love letter to these scanners and still has 0.88 μSv at the high end.
Again though it's not a question of full body does as this is highly concentrated radiation exposure onto high risk tissues.
I think you're missing my point on full-body scanners. As far as I'm aware (at least whenever I've traveled internationally), only a small number of passengers any given day will go through a full-body scanner. Most passengers just go through a regular magnetic scanner which doesn't have any radiation (and for domestic flights in Australia there isn't even the option of a full-body scanner). The point being that even if someone travels four times a week (200 times a year) they still won't go through a full-body scanner (and thus won't be exposed to the radiation from such a scanner) anywhere close to 200 times a year.
Under the current system few people are going to get cancer. But, in the past people where calling systems that where dangerous safe.