Joseph Weizenbaum once said to the question (paraphrasing) "If I don't develop evil/unethical thing Z, someone else will." with: "In city X every day there is rape and if I don't do it, someone else will." Showing how stupid this line of reasoning is.
Which is a different situation than the one with developing some technology. If someone develops faceswap, and then someone else develops it too, we won't have twice the amount of faceswap-badness.
edit: which is not to say that I think "if I don't do it, someone else will" is a good argument for doing something you disagree with..
