On the other hand, it's hard to ignore the fact that typically these people have already profited enormously from these companies and they will never have to face any sort of real ramifications or consequences for the net harm that may ultimately be brought to society.
It's one thing to be sorry, it's another to avoid being complicit in such ventures to begin with. But that's the thing... where is the incentive to "do no harm" in Silicon Valley? There isn't any.
It's an interesting thought experiment to imagine what the world might look like if people were held accountable indefinitely for the externalities caused by the work they conduct.
Not saying this is practical or even desirable, but clearly it would change people's priorities quite a bit. As a software dev there's very little keeping you from accepting a fat job offer from Facebook unless you happen to have a particularly strong & discerning conscious/moral code. I'd like to believe that I'd turn it down... but I'm not so sure. No wonder the world's brightest minds are working at companies like this.