I am dubious about the value of a "public interest" clause as the basis for everything - that tends to be "whatever we agree post-hoc".
Look at medical ethics ideas of "do no harm" - or the more modern interpretation "do more good than harm"
It is perfectly arguable that Facebook has been doing more good than harm. And that is not something one should ban under a code of ethics.
NB
I personally do not think that Facebook's actions have been correct, or worthy or defensible. They have hoovered up everything and left it lying around for anyone to collect - it breaks every Data protection rule set since the 1980s (due care etc). They can and will pay at some point down the line.
But data is like ... oil. It has massive externality costs, but wow has society benefited. From the data footprints we leave we can (if it is well managed(!)) expect improved medical research, improved mental well being, reduction in crime, improved trade, greater econmic equality. Yes there will be costs. And we need to manage those as only externalities can be managed. But the mass collection and processing of our PII data is not just negative cost.
Edit just to be clear this is not an attempt to justify ends with means, or defend facebooks actions - but to note that just because JP Getty was unethical it did not stop ambulances getting petrol engines, generators lighting hospitals and plastics encasing artificial hips.
It's complicated.