I'd say that the onus falls on the engineer insofar as they need to ask the questions of "why are we making the new better tool", "according to what criteria is it better", and "do we need the better tool". And at least for me, that onus falls on the engineer instead of falling on the user because it's the engineer who is creating the tool, not the user, and if the engineer chose differently, the tool wouldn't be out there to be used for evil.

Sometimes it might just be better to not do the thing, especially if it conflicts with one's morals. And well, the idea that "if I don't do this, someone else will" seems to not work out well in practice.