A single engineer at Facebook will not make a difference today. 10 or 12 years ago they absolutely could have changed the course of the company.
Almost all collective change is spearheaded by the ideas and leadership of a few individuals.
Edit: to be a little less terse, in 1996 I quit working for Amazon. There were multiple reasons, some not connected with the company, but a number that were based on my perception of what sort of corporate culture it was going to be have. And yet ... here we are.
Is there anything I could have done in the 14 months I helped build the initial version of amazon to change how things turned out? Is there anything I could have done after that time if I had stayed? Employee #1 had similar misgivings but stayed for 5 years, and was arguably equally ineffective at altering the "nature of the beast".
So sometimes, even though it appears that we do have the power to either (a) withdraw our labor from an organization (b) remain and voice dissent, it ends up doing no good if the actual leadership is following a clearly defined (in their mind) path.
There will always be enablers for the sort of culture that a company like one of the FAANGs want to build.
The people who tend to get power are far from being the most qualified to shape society. People who are good at taking tend to be bad at giving. Shaping society in a good way requires an altruistic (not opportunistic) mindset. Opportunists will constantly see a way to profit and will not be able to resist the temptation. Their personal interests will always get mixed up in their philanthropy so it will never be truly effective. The faith which winners place in the virtues of capitalism is part of the problem.
Ultimately, profit is the product of exploitation. Most successful people will refuse to acknowledge this and that is why they tend to not be effective at shaping a healthy society.
(obviously, razor blades are not a particularly current example :)
It seems like you are painting a picture where Amazon was destined from the beginning to be dealing with the issues it is now. Were there no other possible futures? Were there not individuals who had a massive impact?
I'm related to someone who runs very fairly large warehousing operations across north america. His decisions have certainly been influenced by employees. Hell, I think I've changed his mind on an issue or two over dinner conversations.
I am sure that along the way there have been people inside the company who have shifted its direction towards "better" when viewed from the perspective of society as a whole and the majority of its employees, but those shifts are tiny compared to the momentum of Bezos' conception maintained by suites of VPs etc.
And remember, Bezos et al. almost certainly believe that they are doing the right thing. He might be richest man in the world, but he thinks he got that way by doing something good. He's not so stupid as to imagine the company has no downsides, but I am absolutely certain that he is absolutely certain that Amazon is a net positive for the world.
making a difference or not is a false dichotomy.
Every single candidate refusing to work for fb makes a difference of size one.