I agree marketing is intended to manipulate your thinking... or "market towards you". I suspect I have a different attitude about marketing than you do.
I don't use facebook, I used for a week in 2007, and thought "this is just a marketing data machine, no thanks".
Further, the innocuous sounding "Connecting the world" mission doesn't equate to "monitor your social interactions and help people convince you to buy things" (amongst other things) in most people's minds.
The fact that some people choose to remain uninformed about what Facebook is doing with the data that these people willfully give them is on those people.
What is ethical in this situation is personal to you, so you can't make a blanket statement that marketing is or not ethical.
Again, to me, it's perfectly ethical, but I'm a big believer in personal responsibility.
As you said, you signed up, saw what Facebook was about and bailed.
That's called personal choice, and it's a wonderful thing.
What I think is not ok, and in turn unethical, is for a company to constantly represent that privacy is a top priority, openly say in the press that data will not be sold, and then do it anyway.
And you literally just described the profession of marketing. So if you replaced the inflammatory phrase "manipulate your thinking" with "market toward you", I think they'd be totally fine with it.
I mean, why else do you "Like" something on Facebook anyway unless you want other people to know that you like it?