I think public sphere discussion is appropriate since the foreign policy of a democracy should come from the people. Also while the executive branch is the key player in matters of foreign policy they are dependant on congress for declarations of war (probably no longer relevant in this day and age) and money (relevant in any age).

Military operations do usually delver less than advertised for higher cost but only because people let them. Politicians that promise the absurd and then fail to deliver could be impeached instead we choose to reelect them. Nobody’s fault but our own, but it doesn’t have to be that way.