Facebook, in my opinion, is risky simply because of its reach. It's statistically inevitable that some malcontent is going to see your work and crap all over it just because Mom burned his Pop Tarts. I've also been sexually harassed via Facebook.
But I've had even worse experiences with certain specialized comicbook forums. Of those that still remain, I tread very carefully and rarely there. Whereas Facebook has a whole world of diverse people, some of these specialized forums have all the worst elements of fandom concentrated in one place. I've stopped posting in a couple of them because there was all the petty, vindictive drama of a cliquey prep-dominated high school, but the guys are mostly fortysomething year old creeps who think they know everything.
I love it here. It's kind of like we've got the diversity of Facebook, but we're also all creators still paying our dues, so we're more inclined to help each other out. The fanboys who think it's their masculine prerogative to harass female and other non-cis-male creators aren't here. (If they are here, they have the good sense to not cross paths with me.)