Why Did Milos Forman Change 'Hair' as Much as He Did?

I think we can find an answer in Forman's biography and filmography.

For me, Forman is about one thing (as we can see in Hair and One Flew Over the Cuckoo's Nest), the conflict between an individual and society that claims adjusting and obedience. In Hair it's Claude against the U.S. Army, in One Flew Over the Cuckoo's Nest it's Mac against the mental institution.

The musical was more about the love stories between the members, this hippie utopia and peace movement that goes with it.

But why Forman changed all of this ? Because the war was over when he directed the film, the hippie movement had some shocking events and the story that the musical was telling was about love and music. Which is clearly not what Forman wanted to tell.

So, as an answer, Forman took the background but applied on it his beliefs and he made a film about an individual against the society. Why did he put it in Hair ? Because it gave him the opportunity to mock the American puritanism (family values, conservatism etc.).

I think there are some hints in this interview with Forman.

First, I found this amusing:

O: What about Hair? Did something particular draw you to the play?

MF: Songs. I saw the very first public preview on Broadway of Hair, when I was here in 1967 for some sort of festival or something. I just loved every song. It's one of the three musicals in history in which every song is a gem.

But here he's talking about another film he directed, Taking Off. Notice what he says about hippies in their environment:

I considered a portrait of these young kids, called hippies in those times. But what I discovered... I spent a lot of time in the Lower East Side, seeing these crash pads, and I found them very, very boring. On the other hand, when I talked to the parents of runaway kids, I found them much more interesting, because they were in panic. They were doing things, they were trying to find their children, they were trying to understand their children. The children just spent their time lying in the crash pad, smoking pot and looking at the ceiling. It was very boring. That's why I turned the focus of Taking Off on the parents.

So now it's time to direct Hair; is it likely he's going to retell the story he saw on stage, when he thinks (overall) their lifestyle is boring?

I think instead he looked for ways to introduce conflict, and that started (with a classic man vs man) with Berger meeting Claude. And it's a good setup: a naive, law-abiding fish out of water - soon to be a soldier - meets a gregarious, law-breaking, anti-war rebel. Everything Claude, our protagonist, thought he knew is being challenged.

I agree with what you said about Claude's infatuation with Sheila, but some love interest was necessary in order to provide a reason for the trip to Claude's base. And also to provide the means to get Berger shipped off to war. After all, it was Berger being just a bit too clever and he lost this one.

The really big theme, for me, are the changes designed for the three main characters:

• Claude goes from naive to having his eyes opened.
• Sheila leaves the authoritarian high society and becomes free.
• Berger has to follow rules for the first time in his life.

Despite Forman saying that he liked the music, I think he made the changes he felt he needed to make to keep the story interesting.