The principle is this: military officers and people from families with a military tradition generally tend to strongly support the official line that their country takes in regards to its waging a campaign on foreign ground. That's partly because it's their job to do that (if they are presently in uniform). It's partly because they tend to assume their side is right and the other side is wrong.

Look up the meanings of the words "Principle" and "Stereotype" and tell me honestly which fits the above better. What you describe up above is a "Stereotype":

"a simplified and standardized conception or image invested with special meaning and held in common by members of a group"

"tend to strongly support the official line that their country takes in regards to its waging a campaign on foreign ground. That's partly because it's their job to do that"

No their job and primary purpose is to defend their country from attack. While under that obligation they are perfectly free to individually make up their own minds and form their own opinions regarding "the official line" taken by their Government, they are perfectly free to individually make up their own minds and form their own opinions regarding whether or not they think the Government of their country is right or wrong on any given issue.