As someone who wore their country's uniform (until they kicked me out for being queer), perhaps I can add some perspective.
There's a real emphasis put in the military on being friends with your colleagues. This is because it has long been known that when people fight in wars, they do so not for abstract ideals, not for flag and country, but for the people in the trench beside them. Their buddies.
You never blade your buddy in the army. He or she is going to be the one who has to decide whether to step out into a hail of bullets and haul your wounded ass back to safety...or not.
While there are absolutely camaraderie and good friends available in soup kitchens and other volunteer opportunities, the lack of outside threat means that there isn't the same drive to get along. There's room for drama and feelings.
In uniform, there isn't room for those things. The way of the warrior is the resolute acceptance of one's own death. That makes the job different than almost any other.
Because that's the other secret. You have to care enough about the other members of your side to be willing to put your body in the way of potential lethal harm, in order to do your part in keeping as many of you alive as possible. You try, therefore, to generate a familial feeling within the unit, so that people will have that level of devotion to one another, and will do extraordinary things to help one another. Including sometimes sacrificing their lives to save their buddies. The best way to get someone to be willing to do that is to create that familial feeling.
Is it manipulation? Yes. Are the feelings it generates real nonetheless? Also yes. If you want to look for the conspiracy here, it's in the government failing to provide opportunity enough to young working class kids to make the army an unattractive prospect. If you literally cannot find another way to make a living, then a steady if poor income, with healthcare included, becomes a pretty attractive option.