Open air nuke testing surely produced a generation of dairy cow-keeping farm children with impaired thyroid function. You've pointed out the short half-life of I-131 and that fact, combined with the typical processing times for fresh milk, means that the milk city kids drank was not particularly dangerous. However, the time between our cows eating pasture grass and the milk on my cereal was on the order of two days. Low rates of thyroid cancer and the typically excellent outcomes of care for that should not give the impression that the overall impact was inconsequential. Both I and my sibling have unexplained (i.e. no positive antibody tests) hypothyroidism. Also, I had a super-low draft number for Vietnam, so all of that testing didn't really lower my risk of dying in a war, right?