It's probably a good thing. It shows people that their circles of acquaintance and even intimacy encompass a whole spectrum of views. The strident folks sail in and make ass of themselves, but often do a decent job presenting the side. People you respect surprise you by chiming in the voice of reason on behalf of a side you don't credit with reason.
Facebook is the sociocultural version of early 1980s MTV's play-it-all mix list. By within another 10 years or so, I fully expect to see some "Alternative" surfacing, but for suck's fake, this time I hope they leave the flannel out of it.