Too strong an anti-war message?
An anti-war film, if done well, is far from a bad movie, but only if done well.
If the story (assuming there actually is one) is basically just "war is bad" repeated every ten seconds, it's not going to be a blockbuster.
A good anti-war movie is more than talk. It shows war for what it really is.
While war is never a good thing, it is sometimes the only option, and in fact a fact of life that will never go away, although we can and should try and prevent war as much possible.
Incidentally, this movie was made the way it was when Robert Altman, a WWII veteran, went to Vietnam for some reason and was appalled at what he saw.
It is at this point necessary to put his military service in perspective.
Robert Altman enlisted in the USAAF in 1943 at the age of 18, becoming a bomber co-pilot of a B-24 Liberator and eventually flying in more than fifty missions in the Pacific over Borneo and the Dutch East Indies.
Now I do not want to belittle his service at all, but he was air force, not infantry, so the only part of the war he saw was from the sky, in an area known for fierce guerrilla fighting, but from the air and bombing targets he might not have even seen, so it was not inconceivable that his only exposure to fighting on the ground and what infantry went through was when he visited Vietnam.