Has this philosophical approach ever worked? It's a commonplace in the hard sciences and engineering fields (ie, refusing to work on weapons systems), but weapons systems are elite and well-compensated engineering projects that don't have any trouble finding talent. The same thing goes for NSA, which has a line out the door from elite academia.

I'm not dismissing the sentiment here. It's morally sound. You should act in accordance with your principles and it useful to be reminded how those principles intersect the world. I have similar guardrails (probably not the same as the author's). I just wouldn't want people to overestimate what can be accomplished with this approach.