One benefit many countries get from open source is a political benefit, autonomy.
Now that argument is becoming explicit, a matter of national security. Boingboing reports that the UK is talking of cancelling an order for jet fighters unless they are also given the source code for software used in the jets.
Fast, mobile jets are increasingly based on software. In order to gain performance, designers sacrifice stability, and the controls needed to maintain stability in that environment must become automatic. Thus, software.
The trouble for our military-industrial complex, however, is that having control of the code now means controlling the cockpit. And even the best of friends may part. Note that here it is the UK that is making the objection and the threat. And maybe giving them this autonomy means little.
But what if, next time, it's France? (Fortunately, this picture is of a model plane.) Are you ready for an open source military?