I guess I'd turn it around and ask those developers: Are there any projects you wouldn't do, no matter how much you needed the money, because you found them ethically unacceptable? If the answer is yes, then they actually agree with me, and we're maybe just discussing where the evilness threshold line should be drawn. I don't know many actual people who would say "No, I would willingly work on absolutely any project, no matter how harmful or depraved it is, as long as I get paid," but then again maybe I don't know enough truly desperate people.