I might say more later, but along these lines of, "but what does the movie think of them?" - and something independent of it, that era sure seemed to have a number of general plot lines of, "stranger shows up in messed up environment. One where the powers in charge don't deserve what they have for one reason or another. They shake things up. Then they leave (possibly by death*). You see the effect they've left on others." In this case, I think it was Radar mimicking the whistle at the end.
*: Usually refered to as a Jesus parable in these cases.
I'm just thinking, there was Cool Hand Luke, One Flew Over the Cuckoo's Nest, and this (off the top of my head).
There's probably a few others that I'm not thinking of. Imagining the time I can see why such an anti-establishment archetype seemed appealing to a lot of people. But I have to agree, with what's been said that whatever point it was trying to make didn't seem overly coherent - other than, "our military is fool of buffoons (particularly the leaders), so we should get out of Vietnam,"** and the comic style of people just talking over each other and so many people in a scene that would come to define Altman must have also been very radical. And if this was the only Altman film of that ilk made, that might make it worth consideration... but there are other, better Altman.
**: Just a timeline of other related media I can think of that's broaching this subject (main notable difference they're more, looking back at WW2).
Catch-22 (book): 1961
dr strangelove: 1964
Slaughterhouse-V (book): 1969
Catch-22 (movie): 1970
M*A*S*H: 1970
Sl.-V (movie): 1972