Problem with the ending

I liked this movie overall, but I have an issue with the way the Kothoga dies. Dr. Green yells "Go to hell!" followed by the climactic explosion of the Kothoga. I've heard that this part was added in after test screenings because the director wanted the audience to cheer the monster's death. But did Green not just find out that this was once her colleague? I gather that she didn't think much of his work, but still, I found Dr. Whitney to be more of a tragic character than an evil one that would warrant cheering his death.

He unwittingly drank the soup which transformed him into the Kothoga and regretted it, desperately trying to stop the crates from reaching Chicago. I think having him burn to death as he remembered his true identity would have been a more tragic but appropriate ending. Am I missing more characterization from the book (haven't read it) or is this simply a case of the movie needing a triumphant Hollywood ending where the monster explodes?