Curtis, the villain of the piece, is a villain because he conspires to remove the soul (Effie) from his company's music in order to package it for the white man. And when soul music/Effie attempts a comeback in the mid-1970s, he crushes it with disco.

There's a sharp contrast made between Curtis' world (L.A.) and Effie's world (Detroit) that I don't know if many people picked up on. It's not by accident that Effie's always wearing those Aretha Franklin-issue Afrocentric outfits and hairstyles during the 1970s scenes. She basically represents soul music in the picture, which in real life was reduced and later fully booted out of the Supremes' sound, and most of the rest of Motown's output as well.

The fact that she triumphs in the end is a bit of a fairy-tale ending though, because disco pretty much sounded the death-knell for soul music . But people can dream, can't they?

When I first heard a recording of the original Broadway play, and scrambled to see whatever footage I could, I was appalled at how...right they got the race relations bit, even though a white man is credited with the script (both Sheryl Lee Ralph and Jennifer Holliday have later stated that the original cast did a lot of improv contributions to the script during the workshops, so much so that both believe they should have been compensated.) . The Black characters don't hate white people, they first want to legitimately prove that they've got what it takes to make it just like white folks do. And then when that fails, Curtis resorts to illegal practices. One thing the musical did that the film didn't, which I think the film SHOULD have done, was the expression of Curtis' sentiments about white people and black music in the song "Cadillac Car" (for those who have seen the movie but not the play, the scene where Curtis, Jimmy, and Marty are in the bar discussing Jimmy's sound was originally a song):

Curtis:
"Once upon a time
The Cadillac Car represented
The highest classes in America:
The pure, unstained WASP.
They never worried about the cost, no.
Then the Cadillac was bought by the rising Jews
To show that they were just as good and part of the scheme.
Now we got the Cadillac taken over by our Negro brother
To prove he too belongs in the American dream."

Jimmy: "Marty, this man just handed me a line of crap! I'm dyin' on the charts, and you're givin' me this patriotic rap?"

Curtis: "I'm trying to tell you..."
Jimmy: "Well, you better hurry up, baby!"

Curtis:
"I'm trying to tell you thus:
If the big white man can make us think we need his Cadillac
to make us feel 'as good as him',
We can make him think he needs our music
To make him feel as good as us."

That bit got almost entirely glossed over in the film. But for the most part, the rest of it still gets it right.