True unless you are doing something to concentrate the radiation, like drinking milk from a backyard cow.

http://www.ncbi.nlm.nih.gov/books/NBK100835/

A few important facts for the casual observer.

* I-131 has a half life of 8 days

* statistically significant cancer rate increases are only seen when exposure happened under the age of 20

* cancer risk peaked 15 years after exposure

* the 30-year survival rate for related thyroid cancer is 90%

(don't worry about drinking milk these days)

So if you were a kid at the time, it happened to rain in the short time when atmospheric I-131 concentration was high after a test, and you drank a lot of milk... you had a noticeably higher chance of a fairly low risk cancer around 1980. A real risk to be sure, testing was stopped for a reason, but let's not blow it out of proportion or claim millions of people are still at risk.

And don't forget to notice that your risk of dying in a war is drastically lower as a direct result of these weapons. A direct result of their creation has resulted in relative peace unprecedented in the history of human civilization. War between major powers now seems impossible and old fashioned, though unfounded fear of these weapons was used for decades after WWII as an inappropriate game to control populations and fight-out conflicts between states that could no longer actually go to war.

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?

Vietnam was peanuts compared to WWII, and what nukes did was eliminate the possibility of major wars between advanced states. If nukes were developed at different times, the worldwide war outcomes could have been much much much worse.

It's peanuts unless your particular butt is in a foxhole, then any war is the same.

The most serious fallout damage from a US test was Castle Bravo[1], which had a yield roughly triple the predicted yield, so the damage from fallout was much worse than they had originally predicted. Most of the other tests did not cause significant increases to cancer risk for all but those very close to the tests

1: https://en.wikipedia.org/wiki/Castle_Bravo#Fallout

While true, that doesn't account for the many millions of older people who were exposed to much higher levels of radiation closer to the tests. Many of whom will die of cancers caused by that higher level of exposure.

Contamination from nuclear weapons is not a binary thing. Basically the worst form of contamination is your breathe air with radioactive particles or eat veggies growing in radioactively contaminated soil. Depending on your level of exposure the effects vary widely so pretending cancer is very likely is not really true.