For what it's worth, those 450 "signatures" were just members of an email list. That email list was founded to discuss ethical issues and draft a letter of complain, but discussion quickly fizzled without consensus on issues or solutions.

Then, a month later, this was published out of the blue. No prior communication, no broader input, not even the opportunity to opt-out.

Pretty unethical. As someone who was on that list, that letter is in no way representative... most had pragmatic complaints, like ethical oversight mechanisms to ensure engineers weren't transitively supporting dictatorships. This letter is so hand-wavy, simultaneously cynical and naive.