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.
Facebook offers a service that people wants. A service that is not morally bad, if any connecting people is a positive thing.
The monetization of that business is what has proven problematic. As it is offered for free, it is people's privacy what is being sold.
Who should solve it?
The problem with "just don't work for Facebook" is that it shifts the responsibility to policy companies from governments, that have the power and resources, to individuals that have not. Of course individuals have a moral responsibility, and that is why whistle-blowers are so important in all industries.
But it is the government that has the responsibility to assure that the industry remains a positive force in the country. Tech giants are a new phenomenon. Regulations have not still catch up with its problems. But governments around the globe need to shape up and get up to the challenge of letting companies offer services that people wants and needs while minimizing the harmful impact that some business models have.
If you do not like the ethics of the company that you work for, change jobs. You are going to be happier. But that is not going to make the company more ethical, if any it is going to be less ethical as people that worries about such things move out.