I have my Facebook profile completely locked down from the outside world, and I make sure that what does get out there under my name is stuff I want out there. I am already wary of Facebook to the point that every-time they change something privacy related I feel like I may as well just delete my profile.

While I am intrigued as to how Greplin works I don't think I would ever want to use it because of the concerns you've stated and I myself agree with.