Working for Facebook is a morally bankrupt position. If you are an engineer you have plenty of job opportunities available to you and there is no excuse for you to continue contributing your labor and time to a wholly malignant organization. At a certain point one has to ask how we as an industry will start dealing with those who continue to take a paycheck from Facebook even in the face of constant and horrific evidence of wholesale ethical violations and negligence.
So they are certainly engineers at Facebook doing very questionable things - but not all of them.
In general: the more influence you have (via code you write or otherwise via power you are aware you have over people), the more you become ethically accountable for your actions.