It’s true that in 1939 they didn’t know how to split an atom. They also didn’t know how to teleport, or travel backward in time, or do many other dangerous things. Should they have worried about those, too? What percentage of futuristic technologies ever gets developed? What percentage gets developed soon? It might be rational to worry about an unknown future, but it’s irrational to worry about one specific scenario of doom unless you have lots of evidence that it will in fact happen.
It’s true that in 1939 they didn’t know how to split an atom. They also didn’t know how to teleport, or travel backward in time, or do many other dangerous things. Should they have worried about those, too? What percentage of futuristic technologies ever gets developed? What percentage gets developed soon? It might be rational to worry about an unknown future, but it’s irrational to worry about one specific scenario of doom unless you have lots of evidence that it will in fact happen.