So not only will someone else do it, if you join, there will be even more harm. So don't do it!

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..