Refusing to participate WORKS.

I've had the unfortunate experience of working at a startup that started courting some autonomous weapons companies and HOLY SHIT were they the bottom of the barrel. Levels of incompetence you wouldn't believe, just good ol' boys who wanted to play with energetics. Then the company I was working for also hemorrhaged all their top engineers because they found the work unsettling.

The takeaway is that your refusal to assist these shitheads does have an impact, they have to pay more for talent and they have a much harder time courting good talent.