https://www.computer.org/web/education/code-of-ethics
None of it gives Facebook engineers any comfort.
They are responsible for the fruits of their efforts. Recent revelations are of degree, not kind. The consequences of engineering work were reasonably foreseeable and the consequences were not at arm's length. Facebook's business model has been clear and well-understood for years and years now. This is not technology being misapplied by someone several steps removed from you. This is technology misapplied by Facebook and Facebook's immediate customers and Facebook engineers enabled it.
Technology work has dimensions beyond "it's interesting" and "they pay me a lot". I hold us as professionals. We have duties which go beyond our own self-regard.
I am unsympathetic to anyone at Facebook feeling moral disquiet. I think you know what you ought to do.