I think of something like legal or medical confidentiality, which can involve their clients doing pretty horrible things but it being the "ethical" thing to not reveal that. If one takes this same thing to a Facebook scenario, does the developer who works for Facebook then have the obligation to protect the confidentiality of Facebook even if they're doing awful things? Would it be any different where a lawyer is working for a horrible client, trying to use the law to do things that are a net-negative for society, but ethics would put their obligation towards their direct client rather than society at large.
If one then wants to write a piece about ethics, one should start with examples of fields with ethical codes that have a structure closer to the relationship of users/Facebook/developers.