Every parent should watch their children's social media accounts. I have made my daughter remove friends and some posts simply because I felt they were out of line. Fights between people should remain private unless it's your teacher or a boss. When it come to a work issue you could get fired so that's an individual choice. If friends are just bad news then they should be removed. I've removed my own friends because I don't like a post they made I considered humiliating or berating. It isn't asking the child to do something I haven't already done.
However when they become adults you can't tell them what to do but it doesn't mean you can not mention something you saw that appeared offensive and have a deep discussion until they agree to remove it. There are ways of handling things. But what happens when you spy and find something that was completely unexpected . Something that made you sit back in that unexpected, mouth gapped, awe struck feature that if someone walked in at that moment they would have to say 'What happened?'
Then you would smile responding 'Something good'
That's what happened to me while stalking my 21 year old daughter and I found she posted a particular meme.
Sometimes it's worth looking through the Facebook thoughts of your kids!