A nice excerpt in The Hollywood Reporter from the new Sherry Lansing biography. It's about when she was producing Fatal Attraction.
The point of the film was actions have consequences, and the earlier ending had Douglas paying for what he did. (Close didn't fare well, either.) The studio made it clear--scrap that ending, kill Glenn Close and save Douglas.
It went against the point of the script, and Close refused to do it. Ultimately, everyone had to suck it up and give the public what it wanted. Filmmakers may have a message, but if they want a hit, sometimes they have to bend to audience demand.
Sure enough, the new version of the film was a blockbuster, nominated for numerous Oscars and helping everyone's career. Was it worth it? The people who made the film have to decide that for themselves. I think the new ending makes more movie sense, even if it's less subtle and turns Close into a psycho who must be terminated.