[nl]

I'd normally be with you in defending Facebook here, but in this case the ethics really are questionable.

They designed an experiment where there was a serious hypothesis that it could lead to depression in the people subject to it. That has the potential to be actually harmful.

I still defend Facebook's right to do research, but they need to take more care to avoid harm.

The industry as a whole doesn't perform experiments designed to depress people. There could be other unethical experiments too, but they need to be judged on a case by case basis.