Has there ever been a case of inappropriate relationships between teachers and students that couldn’t be traced back to a social media connection?  There’s a lot of bad stuff out there and such tools are a distraction from learning at the least and a potential for real harm at worst.  How would you monitor and control it?  You can’t.  You can only teach students what is right and the respond when they choose to do otherwise.  There are other tools, such as MBC, that offer the same social components but provide the safety net that can protect students while also teaching them to behave appropriately.