I always opt out of backscatter, but at this point absolutely do not opt out of MMR + ATR.

Reasons:

1) Privacy - MMR + ATR is less invasive to me than a grope. Neither is ideal.

2) Safety - While there is certainly an unknown factor, there is no theoretical basis for MMW being dangerous. If I were to have a problem with MMW, to be consistent, I would also have to have problems with many other items in daily use that also emit non-ionizing irradiation (including cell phones, wifi, etc.) If MMW is dangerous, some of these would be even more dangerous.