In the past week, I've decided to change the way I deal with Facebook. I used to put up posts on a "political hot potato" topic. I have to stop. I find that's where most of the issues take place within my circle.
Also, be aware that Facebook DOES allow for private/secret groups. I belong to one to discuss specific issues pertaining to my upbringing. It is closely monitored by the group founder for trolling and has a list of rules that you have to agree to follow before you are admitted. And it is hidden from public view ... so you join by finding this person's blog initially, then sending her an email, then exchanging an email about why you want to be admitted, THEN she approves you, then it's up to you to "join" the group ... and no one in your circle can see that you're in it or that it even exists. It's perfect if you need to vent in a healthy way.
Probably the best rule of thumb for Facebook is not to post anything that will attract bullies or trolls ... and if you have something nagging at you, find a supportive "secret" group where the comments are handled with compassion and without judgment. It's tough, but doable. I will say, it's extremely helpful for me personally.