> But really, do we want to look for ethical advice from a guy who worked on explosives for the military and then moved on to bring about the most destructive weapons that have ever existed?

We frequently faced with questions of what we ought to do. Should we take Interstate 80 or Interstate 5? Should we eat a high-carbohydrate diet or a ketogenic diet? Should we pursue dating Barbara or Debora? Should we invest in hydrogen bombs or a larger army?

There are right answers and wrong answers to these questions, as well as answers that are in between. Which answers are right and which answers are wrong depends on two questions: first, it depends on which means will produce which results; and second, it depends on which results would be in accordance with our ends, and which would be destructive to our ends.

So, to decide whether to take Interstate 80 or Interstate 5, we must first decide whether we want to go to Santa Cruz or to Sacramento (assuming we are in San Francisco), and then consult a map. The map will tell us whether taking Interstate 80 will have the result of getting to Santa Cruz or not. Then it is of great importance whether the map is accurate and covers the area in question, and of no importance whatsoever that the mapmaker wanted to go to Sacramento, while we want to go to Santa Cruz.

Von Neumann provided an extremely accurate map of the consequences of the hydrogen bomb to the government of his time, as well as the chances of success of various ways of achieving nuclear fusion. The people that followed his advice were able to achieve historically unprecedented military power, which was their intent. If von Neumann's map had been inaccurate, they would have failed and sunken into irrelevance, like our own Project Huemul here in Argentina, which never succeeded in achieving nuclear fusion. The fact that you yourself do not want to create powerful weapons and achieve military victory is of no relevance whatsoever.

The failure of the peaceful nuclear-energy Project Huemul, particularly in the context of the rather heavy bets we had placed on it, was a significant step in Argentina's decline. It was precipitated in large part by the president emptying the academies of his political opponents, depriving his projects of the accurate and brilliant guidance he needed to make good decisions about questions of science. Perhaps, for all their smarts, they were unwise to oppose the president. (This error was repeated by later military dictatorships, further into Argentina's decline, who expelled and sometimes killed the partisans of the banished former president; the University of Buenos Aires, among others, still keenly feels the loss.)

Of course it is possible for a map to be correct about one such factual question and erroneous or silent about another; no map of Argentina will tell you how to get to Bakersfield, and an unreliable map might mislabel Interstate 80 as Interstate 70 despite correctly labeling Interstate 5. But you have given no reason to suspect that von Neumann was inaccurate about the likely results of self-reproducing machines (and, in case you haven't read him, gray goo and Skynet are not similar to what he predicted); you have merely labeled him "unwise" because, at least on questions of nuclear disarmament, he would have been your political opponent.