Preface: I totally agree with your argument that risks must be weighed against outcomes. I also believe that even if the scanning technology were totally safe, it would be objectionable on privacy grounds. I think we're going about the whole problem of security backwards. :)
An increase that is so minute that we don't mind the dentist or doctor X-raying us.
Actually, we do. There are good reasons we impose strict limits on your medical X-ray exposure annually, and why you wear a lead vest or use collars to protect other tissue. There's also a good reason the radiologist stands outside the other room to press the button. Two x-rays a year is not significantly mutagenic. Fifty? Then you start getting nervous.
Not WiFi or the low-energy spectrum of the sun. What energy is 'low' in this respect?. And how long is 'prolonged exposure'
UV exposure from solar radiation is one of the biggest melanoma risks. A few orders of magnitude up the frequency scale, X rays for far shorter durations also have mutagenic effects on skin tissue. It's possible that low-energy X rays, falling in the middle of that energy range, also cause cancer. We don't know for sure yet because we don't regularly expose people to them.
(I should mention that just because the X rays are low energy does not mean their effects scale linearly. Medical X rays are well above the Compton shoulder. IIRC (not enough time to check now) they're thermalizing slowly in heavy tissues as opposed to bouncing inelastically off the surface layers. Depending on the scattering cross-section for those energies, the backscattered X rays could be more ionizing. Total conjecture... I haven't done this for a while.)
Again, the problem is a slightly increased risk. But why is that increased risk a problem in the first place?
You're absolutely right. We have no good characterization of the risk. Radiation biometrics is fucking hard. I only want to argue that our current risk statement is inaccurate and poorly understood (for instance, we don't even know the angular flux of these machines), and offer some potential reasons why the risk might be higher than currently stated.
An increase that is so minute that we don't mind the dentist or doctor X-raying us.
Actually, we do. There are good reasons we impose strict limits on your medical X-ray exposure annually, and why you wear a lead vest or use collars to protect other tissue. There's also a good reason the radiologist stands outside the other room to press the button. Two x-rays a year is not significantly mutagenic. Fifty? Then you start getting nervous.
Not WiFi or the low-energy spectrum of the sun. What energy is 'low' in this respect?. And how long is 'prolonged exposure'
UV exposure from solar radiation is one of the biggest melanoma risks. A few orders of magnitude up the frequency scale, X rays for far shorter durations also have mutagenic effects on skin tissue. It's possible that low-energy X rays, falling in the middle of that energy range, also cause cancer. We don't know for sure yet because we don't regularly expose people to them.
(I should mention that just because the X rays are low energy does not mean their effects scale linearly. Medical X rays are well above the Compton shoulder. IIRC (not enough time to check now) they're thermalizing slowly in heavy tissues as opposed to bouncing inelastically off the surface layers. Depending on the scattering cross-section for those energies, the backscattered X rays could be more ionizing. Total conjecture... I haven't done this for a while.)
Again, the problem is a slightly increased risk. But why is that increased risk a problem in the first place?
You're absolutely right. We have no good characterization of the risk. Radiation biometrics is fucking hard. I only want to argue that our current risk statement is inaccurate and poorly understood (for instance, we don't even know the angular flux of these machines), and offer some potential reasons why the risk might be higher than currently stated.