Many tech engineers are extremely principled, to the point where it would be impossible to pull something like that off without someone finding out about it and blowing the whistle.
I don't think engineers are more principled than others, and thinking we are exceptional is, IMHO, the number one way to expose ourselves to these human frailties.
So I'd like to add to your rebuttal that extremely principled people are also capable of awful actions. All it takes is a good theory.
It's not about nobody finding out about it. It's about having enough people in key positions who are OK with doing it.
Extremely principled about who should win the election.
I don't want to turn this discussion into the presidential mess, but it's no secret that virtually almost everyone working for a particular search engine, from employee to executive support one particular candidate and not the other.
A small group of people here are very vocal about who they support, but probably 90+% of people never mention politics and don't seem to like to talk about it at work.
I guess I'll say I only know the google model of things, where pretty much 99.9% of the codebase is open to FTEs. It would be very very difficult to slip anything into the code there without someone catching on and causing a shitstorm.