The real reason behind such a move is the culture of litigation in the US. Someone made your coffee too hot? Sue them. Someone stepped on your toe? Sue them. In this case, everyone is ducking for cover because they don't want to be the focus of a lawsuit that claims they didn't do anything to prevent the spread of the disease. The people who make these decisions at MIT are not unintelligent. They have all the resources and risk models at their disposal. They have obviously found that the financial risk to the school is greater if they don't send all the students away vs if they do.