Facebook has become the most toxic social media venue out there. I've gone mostly to instagram almost entirely for photos. It is amazing how much extra odd stress disappears without reading toxic FB arguements. It's like the outlet that people take all their anxieties out on.
But I agree, if things posted to Facebook start changing your perceptions of a place, it's time to go. If I look at any of the Vermont news stations like WCAX and read the 500 comments posted under a headline on FB, I would not believe that is the same Vermont I live in (and an outsider reading it might be like, "this state is supposedly progressive?"). It's just all hate all the time, on everything. People just shouting at each other.
The best idea is to just go out and live.