Even more troubling than Aliens, Russians or Chineses, would be if those devices were NAZI UFO, or worse, non-homo-sapiens-sapiens devices (say, remnants of some ancient civilisation that lives hidden on (in) Earth.
Mistaking optical illusions, camera and radar artifacts, etc. for strange aircraft would also be very troubling: ignorant pilots, inadequate equipment, unprepared scientists and engineers...
This guardian article is perfect example how to keep hype going. You get few non-experts from pentagon to talk hypothetically in very general level about things not exactly in their area of expertice. Then astronomer pours cold water.
