It had occured to me that perhaps Groves and the others realized that they had gone too far in promoting their imaginary atomic bomb as a wonderful weapon. The general public began thinking up a lot of good uses for it.
During Vietnam, people said, "Why don't they just drop the bomb on them?" And even during the Iraq invasion, people said,"Why don't they just nuke them?" It may have surprised the Manhattan group that White Christians didn't have any reservations about obliterating non-white, non-Christians. And why be afraid of a weapon that only you possessed?
Realizing that the public might start demanding the use of the atomic bomb, which of course couldn't be realized because it didn't exist, they had to think up reasons not to use the bomb. So I can imagine a four prong method:
1) Promote this radiation stuff, that drifted with the wind, so that an atomic war could never be localized, but affected everyone around earth.
2) Promote the 'brotherhood of man' in all the Christian churches, so that white Christians would have some reservations about bombing someone halfway around the world. (I don't think this has worked so well, really.)
3) 'Leak' the plans for the imaginary weapon to the USSR and other places. Develop Mutually Assured Destruction. So the weapon isn't yours alone anymore.
4) Juice the weapons up to such a size, and say there are so many of them, and talk about how many times over the earth could be destroyed.
Thus making nuclear war 'unthinkable'.
Very ingenious point, worth repeating. At the time, late 50s/ early 60s, Bertrand Russell was saying something like '... modern science has made it inevitable that all must live or all must die.' This seems an odd claim, since hardly any countries were supposed to have the things. But if there's huge destruction and radiation, and moreover if shelters are stated to be more or less impractical, then neighbours and other countries get harmed, too. Also it made it necessary to have leaks to the 'Russians', i.e. Jews controlling the Soviet Union, which of course is the sort of thing Jews do habitually on auto-pilot. It also made it necessary to oppose Senator Joseph McCarthy and generally agitate in favour of supposed spies - if the issue really had been that serious, it's hard to imagine anyone being lax about it. (Similar thing with AIDS of course).
Russell (apologies to Americans - I'm a sort of fan of his, but I think his impact in the USA was less than here) is now known to have been fed information from British official sources, and it's hard to know how much of it was Russell giving his own views, and Russell trimming to e.g. suit his view of world government. The info to him must have been rather secret - Denis Healey says in his autobiography that he visited Russell to quiz him on nuclear issues, but wasn't impressed, suggesting various branches were doing their own things.