The whole developement of nuclear weapons is a story of the when, of the how fast and of the should I and would have looked certainly different if it’s protagonists all had based their decisions on the ethical rationalisation you proposed here. Who knows, maybe even the Germans would have gotten nuclear weapons?
The hard question obviously is: where do you draw the border? If you invented the paperclip and it was beeing used in the holocaust’s bureaucracy blaming you would be a bit far fetched. If you invented the gas showers of the KZs whose only purpose it was to mass-kill prisoners, not feeling ethically responsible would be totally mad. In between there you have got Werner von Braun with his V2 rocket, which isn’t exactly easy to judge. He enabled space travel, yet the bombs killed many british civilians quasi randomly and out of the blue and the number of slave workers killed during construction was even higher than the number the rocket killed.
Inbetween these three examples there are infinite shades of ethical dilemma while your argument paints this as a binary question about whether something could or should exist or not — and if the answer to the could is True, who cares about the answer to the should, right?
I propose something else. If you value your own intellect you should abstain from ideas that could be, but shouldn’t and rather attack things that could be and should be or maybe even things that should be, but couldn’t by the thinking of today.
We engineers, scientists, thinkers and artists are giving birth to things that become reality, but it is our indivisual decision if we do:
You will rarely find a writer telling you he had to write that dehumanizing dangerous text, because if he wouldn’t have done it somebody else would have. We can stray farther from this even and paint an example where a old lady collapses at a bus stop. Now you could have someone robbing her as she lays there (”If I wouldn’t have done it someone else would’ve”). Or you could have somebody going for first aid and calling the ambulance (”If I wouldn’t have done it someone else would’ve”).
The statement “someone else would’ve done it” is not really a ethical reason to do anything. The question you should ask yourself is: in what kind of society do I want to live and do my actions contribute to it and if so at what cost? What if everybody acted like I did?