Anything involving Facebook is going to raise privacy concerns, but the company claims to have this covered. You should also take advantage of your own friends by asking around to see if they belong to any secret groups that might interest you. So, what sets it apart?
The thing is, in addition to the open groups, there are closed and secret Facebook groups too. How will Facebook police that? That demographic is already more likely to be single, and maybe they'll be more likely to use Facebook if it has an official dating service.