He says it may not be a good idea to make ourselves known 'out there'. Contacts between advanced civilizations and lesser have never worked out well for the lesser.
That is a plausible explanation why we can't find anyone out there. They are all in hiding. In general for advanced intelligence to form faster than meteor impacts hit, the high speed evolutionary pressure of tribal warfare is necessary. That's certainly been the requirement on planet Earth. The Milky Way should probably be renamed Martin Luther King Jr. Galaxy.