It's not because one doesn't think it's unethical that it is ethical. The very existence of the question implies that there is an ethical issue here. Moreover,

It's not because one doesn't think it's unethical that it is ethical. The very existence of the question implies that there is an ethical issue here. Moreover, in the age of information, the one who knows more about the other becomes a potential predator (every country has secret services and spies). Facebook (and others) knows a lot more about me than I do myself because their computers don't forget, because they analyze what I do in a way I don't. Moreover Facebook can be tied to other companies or institutions with my consent. So although the optimization might seem like a good idea, I think it also needs to be put in context. Is this really a good idea. Is optimizing advertisement a noble goal ? It's useful for the advertisers, true. But is it useful for their targets ?