Facebook uses all this data to show you ads for things you might want to buy. Wouldn't you rather see that than ads for things you don't want to buy?
I occasionally watch the evening news and I am sick and tired of ads for drugs for old people. I'm not old and I don't need drugs. But the television stations can't target their ads at specific viewers (yet) so they target them at demographics. And old people tend to watch the evening news more than other demographics so that's what they show.
People act like Facebook (and every other company) is gathering data about people for some sort of nefarious plan for world domination. But all they're doing is improving the quality of connections between people making things (advertisers) and people who might want those things (consumers). Is that really so terrible?