The argument is presumably that if you won't do it, they'll find someone else who will.

That's a pretty shit argument for being the one who folds. If everyone does refuse then it doesn't get built. If you refuse and they find someone else, that person may not be as good as you and may create a less effective surveillance apparatus which is easier for white hats to neutralize or dismantle.

Engineering has practical consequences. If you build something that gets democracy activists killed, you're the one who has to live with that. There are plenty of cool problems to solve that don't involve the construction of a surveillance state.