It looks like you answered your own question, but they also change the theme of the story from one of abandonment, control, and approval/validation.
Frankenstein creates his monster after his mother dies, leaving him feeling abandoned.
His creation is an attempt to give life without the need for a woman (controlling life).
The monster spends much of the story seeking validation from his creator, who wants nothing to do with him. In some sense, this parallels Victor's inability to cope with his mother's loss, except that Victor is still very much alive. I'm sure many people view this as a religious allegory (God abandoning humans).
I don't recall catching any of that in the movies. Instead, they turn it into the typical battle against the unknown/unfamiliar. The monster is not understood, and is grotesque looking, so the people want it gone. Of course, none of the pitchforks and torches are ever carried in the novel.
Of course, there's also the issue of Frankenstein's presentation on screen. In the book, he's clearly described as being yellow; yet, in most of the movies, he's green. Oh, and Frankenstein never yells "it's alive!"