> Can we assume that anyone who has worked at any of those companies has at best dubious morals, or are they instead small players in a big machine?

Why not both? They certainly are small players in a big machine, but the reality is that any engineer capable of getting a job in FAANG has plenty of other options that are less morally dubious. If they chose FAANG in spite of this they either don't believe it's immoral or are willing to look the other way for money/prestige.

I certainly wouldn't advocate for writing people off entirely based on their work history (after all, it could be that they went in not realizing the extent of the harm and that's why they're leaving), but I do think it's a factor worth considering.