The poster you quote believes that Facebook is clearly immoral, and to continue to work there is indefensible.
Have you considered that this might be true?
Now perhaps you don’t think it is true. That would be my guess based on your positions in this thread.
A non-absolutist position would be to say ‘Facebook as a whole isn’t that bad - here are my reasons...’
Whereas your actual position is ‘nobody can make valid ethical statements about organization above a certain unstated size’.
The first is holding a different opinion. The second is an absolutist claim.
Another counterargument could be like the Nuremberg defenses that you have already mentioned - I.e. Facebook is that bad but there are good people there who don’t realize that, or who think they can change it, or don’t understand the consequences of the orders they are following etc.
But that’s not what you are saying - you are saying that nobody should claim that Facebook is that bad.
You seem to think that Facebook is no different from any other employer, but have offered no explanation other than to suggest that not all steps taken by all employees are calculated to be evil.
It’s perfectly reasonable for others to think that Facebook is so obviously corrupt that to work there is morally bankrupt.
Perhaps it is.