the distilled version of any of the arguments is "I think an AI with X capability is dangerous to the world at large." -- and they may not be wrong.. but as OP pointed out : that doesn't really stop other developers with less qualms from tackling the problem.
All that abstaining does is ensure that you, as a developer, have little to no say in the developmental arc of the specific project -- for a slice of peace knowing that you're not responsible.
the problem really arises when that slice of peace is now no longer worthwhile having in whatever dystopic hell-world has developed in your absence..
(.. not to say that i'm not hopeful.. )