These comments come up from time to time. Like anything, if you use it properly it can be of help and interest. Make your settings secure, so friends only can see. Do not accept people as friends who you don't trust or want to "have a nose" at your activities. I ignore friends requests from most people at work. IF anyone ever was horrible/bitchy etc I would delete them, but as I am choosy who I accept as a friend, that has never happened.
I am a member of quite a few private groups specialising in my interests. Local wildlife, crafts etc etc. - you can learn so much from people this way.
I am also a member of some local FB groups, and they are useful too. Those members cannot see any of my private life posts, just the ones pertaining to that group. Sometimes I will ask for recommendations locally if I am searching for, say, a good car mechanic, or painter etc.
I use it for my cat charity to advertise lost cats locally, or to find homes for cats.
I sell items locally at no charge on market place, and can buy.
I keep in touch with distant family and friends. I have a couple of private message groups (just 4 old friends) who chat privately. It can be a godsend for people who are a bit lonely, especially with the lookdown.
So don't dismiss it in a disparaging way just because you have read scare stories. Maybe it's not for you, but the picture you paint is not the truth for me at all.