Facebook on the other hand is not inevitable.
Should Facebook employees always be concerned with the ethical consequences of their work?
I think your argument is that the ethics means we really needed enough nuclear weapons to destroy the planet several times over?
And we really needed to let the government sell the lie that there was a 'missile gap' to the US population? Or was that lie in order to hide that there were U-2 overflights? Who were we hiding the knowledge of U-2s from? The Soviets, who could see them on radar and were developing ways to shoot them down? Or the US public?
It's all very odd ethics. I'm sure the Rand Corporation has some game theorists who would clear everything up.
From memory the "missile gap" wasn't a government lie to hide anything but an election campaign lie by Kennedy to attack the govt and appear tougher on the "commies".
https://en.wikipedia.org/wiki/Missile_gap
> According to Robert McNamara, Kennedy was leaked the inflated US Air Force estimates by Senator Stuart Symington, the former Secretary of the Air Force. Unaware that the report was misleading, Kennedy used the numbers in the document and based some of his 1960 election campaign platform on the Republicans being "weak on defense."[5] The missile gap was a common theme.
> Eisenhower refused to refute the claims publicly for fear that public disclosure would jeopardize the secret U-2 flights. Consequently, Eisenhower was frustrated by what he conclusively knew to be Kennedy's erroneous claims that the United States was behind the USSR in its number of missiles.[6]
> In an attempt to defuse the situation, Eisenhower arranged for Kennedy and Lyndon Johnson to be apprised of the information, first with a meeting by the Joint Chiefs of Staff, then Strategic Air Command, and finally with the Director of the CIA, Allen Dulles, in July 1960. Still, Kennedy continued to use the same rhetoric, which modern historians have debated as likely being so useful to the campaign that he was willing to ignore the truth.
If you want an explicit lie, the Eisenhower administration lied to the US public saying that the U-2 was for high-altitude weather research. When Powers was shot down, the official US lie was that a high-altitude research flight was missing, and may have 'drifted with an incapacitated pilot across the Soviet border' - https://en.wikipedia.org/wiki/Lockheed_U-2 .
If the Manhattan Project is a useful comparison, then we have to take the totality of the people working on project, including the one person who quit, for moral reasons.
He 'believed that scientists should always be concerned with the ethical consequences of their work'.
In other words, yes, we should apportion some blame to 'the scientists of the Manhattan Project for dropping the atomic bomb'.
(For that matter, Philip Morrison was one of those scientists. He helped load the atomic bombs onto the planes that made the two bomb runs. Certainly there's direct blame there, if blame is to be placed.)
Certainly the rest of the scientific staff did not have the same views, or at least, didn't place the same weight on the different aspects of the ethics.
Even then, remember that Oppenheimer remarked that he felt he had "blood on my hands" because he and others of the scientific staff thought the bombing of Nagasaki was unnecessary. Truman later told Acheson "I don't want to see that son-of-a-bitch in this office ever again."
Regarding your point, and quoting from the WP page on Rotblat: "Rotblat continued to have strong reservations about the use of science to develop such a devastating weapon. In 1985, he related that at a private dinner at the Chadwicks' house at Los Alamos in March 1944, he was shocked to hear the director of the Manhattan Project, Major General Leslie R. Groves, Jr., say words to the effect that the real purpose in making the bomb was to subdue the Soviets."
I interpret that to mean that Rotblat would have considered using the bomb against the Soviets in the way you summarized it as being sufficiently unethical that he would not work on it.
Consider Joseph Rotblat. He worked on the Manhattan Project because believed that it was needed as a deterrent against a German nuclear weapon. After he learned that Germany had given up on the bomb, he left the Manhattan Project - the only one to do so - and felt betrayed by its use in Japan.
"Rotblat believed that scientists should always be concerned with the ethical consequences of their work.[39] He became one of the most prominent critics of the nuclear arms race ... Rotblat shared, with the Pugwash Conferences, the 1995 Nobel Peace Prize for efforts toward nuclear disarmament." - https://en.wikipedia.org/wiki/Joseph_Rotblat .
There's a movie about him, "The Strangest Dream", at https://www.nfb.ca/film/strangest_dream/ .