What a lot of people confuse the medium with the message!
Facebook is only another means of communicating, like letters, postcards, greetings cards, telephones, magnetic noticeboards, music requests with loving messages, banners towed across the sky etc etc etc. Plenty of nasty messages can be sent by old-fashioned letter or said over the phone. No-one curses the telephone because someone has shouted at them over the line, or decvlares that they are never gouing to write another letter to anyone because of what was written to them.
If Facebook friends post hurtful things, it is because those friends typed in the words - Facebook itself didn't. Or perhaps they just typed in something that wasn't meant to be hurtful at all, but was misunderstood.