Didn't Altman himself say it wasn't an anti-war film?

I'd say it's probably more anti-authority than anti-war. The TV series was probably technically more "anti-war," by definition. It had more humanity to it.
This movie was based off Richard Hornberger's novel, "MASH," which was pretty good. But the novel wasn't anti-war at all. Maybe a little bit anti-authority. In the novel the charactersincluding Hawkeye and Trapperare politically incorrect, say sexist and racist things and they have a "My countrywrong or right!" attitude. They have no profound statements to make against the war, just like how they don't in the movie. But still the movie was released at a time when people were angry about Vietnam so an irreverent movie about another war was a breath of fresh air for many people.

There is not a single pro-war person who had their mind changed by this film.
I have never heard of a serious film maker deliberately setting out to make an "anti-war" film, so I think your claim that MASH does not succeed as an anti-war film is a good one!
Likewise, writers don't effectively sit down to write "anti-war books." It's only the people who seek to classify things who adhere to the silly concept of anti-war books & films.

The thing that failed to make this film anti-war is (the) fact that the film is set
in (the) Korean War.

Altman's original intention was that the film be about the Vietnam War, as much as a film shot in the southern California desert can be. It was the studio who made him add the crawl at the beginning setting it in Korea.
Any work that deals honestly with war is inherently "anti-war" and no-one who thinks
seriously about war is "pro-war". Some wars are justified, some not so much.

The thing that failed to make this film anti-war and ,,change my mind'' is fact that the film is set in Korean War. Which was one of (If not the most) the most moral and just interventions in history. (Like II World War Korean War was also started by totalitarian dictatorship which must have been stopped by any means)
,,There is not a single pro-war person'' thats right. I seriosly doubt whether there is really a person who is ,,pro-war''. Everybody is anti war, but some wars are just sad but necesseary duty (Korean War was one of them)

Maybe they should turn it into a TV series.
Nah, it'll never work.

Please Mr. Miw, don't be disingenuous, it's beneath you. I never called you a "prick."
I merely said you sounded like one.

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Fair enough, I did go full Trump.
Let's step back and review: I post a negative review of the film. No personal attacks, just a negative review. Let's review the responses:
Craig: "you have to be a grown-up with a sense of humor" to like it.
Cruff: called me an beep and prick
You: called me poindexter
Spooky: brought my mom and dad into the discussion
Me: went full Trump.
Yes, of course I am the problem. I went full Trump after being personally attacked by a bunch of strangers for merely posting a negative review of a film. Sure, I'll sign off on that. I am the immature one. Responding to movie reviews with personal attacks: the definition of maturity. Thanks!

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Yeah, you sound like just the type of ass hole loser who this film is made for. Why don't you go and deliver any further pronouncements to your obese wife. I'm not interested.

You're always entitled to your opinion, sir.
But so am I. And in my opinion, you sound like a real prick with a 10 ft. 2 by 4 shoved up your ass. Have a nice day.

Yeah, they should lighten up. War is tons-o-fun!

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Yet not too young to get Shampoo, The Player, McCabe and Mrs. Miller, Citizen Kane, Vertigo, Dr Zhivago, Touch of Evil, M, Lawrence of Arabia, Days of Heaven, Mean Streets, The Deer Hunter, The Graduate, Singin in the Rain, All About Eve, Chinatown, Dr Strangelove, Barry Lyndon, Midnight Cowboy, Easy Rider, The Third Man, Bicycle Thieves, Pierre le Fou, Jules and Jim, etc, etc, etc times infinity. Amazing how I was able to "get" all of these old movies but somehow MASH eluded me. It must be the most brilliant film ever made, I guess, and my own brilliance finally found its natural limit.

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I've spoken with at least 2 other grown-ups that also didn't find it funny.
Yeah, I know, your mum and your dad and let me tell you they were nodding their heads to appease you.
Yes the film has a cynical tone and that contributes towards its terrific sense of humour.
Negative never! Col. Blake and the 4077th make an art form of turning negatives into positives.

Rage-filled snobs and ass holes who think this is an awesome film? is that the flock in question? (I'm referring to most respondents in this thread, not all fans of the film)

Ass holes of a feather flock together.

You found 2 other people who didn't think this funny?!?! Well, that's conclusive proof. It's not funny.

I am a grown-up. It's not funny. I've spoken with at least 2 other grown-ups that also didn't find it funny. It's pretentious, condescending and cynical.
I am a huge Altman fan. I love The Player, McCabe and Mrs. Miller, etc.
The Player was cynical but it was fun. McCabe and Mrs. Miller was cynical and dark. MASH is cynical and mean-spirited.

This was an anti-war film? I thought it was a flip-the-middle-finger-at-the-establishment anti-draft film. Much more effective as that.
And it was funny, but you have to be a grown-up with a sense of humor. I never used to think it was funny, but that was when I was 10 and laughed at the TV series (which was mostly funny only because of the canned laugh track).