He declined to discuss in detail just how much damage an attacker could do with the aircraft hack they pulled off, saying: "This has to be explained carefully, and we've got all the technical details backing our claim. It's not an apocalypse, but basically there are some scenarios that are possible" that will be covered at Black Hat, he says.
What he's saying is this is one piece of the puzzle that could be part of a plan to do something nefarious. To say it's not dangerous is dis-ingenious, but to claim "airliners remotely controlled!" is too.
I would suggest that access to in-flight systems be controlled by applications that require 2 factor authentication before this gets out of hand.
To attacks like this, authentication might as well not be there. Most hacks operate this way. The real world example is you put enough weight on the door and it opens instead of using the key, or you turn door knob furiously left and right until some part breaks inside.