Finally, after a lengthy court battle, the child is placed into proper care with his real dad. It's easy to forget that Sonny didn't win that court case; the real dad, played by Jon Stewart, swooped in and saved the day just like he does in real life. But, just before that, the judge found Sonny unfit to be a parent.
The movie positions Sonny as the hero we want to watch succeed and Arthur as, essentially, an evil child snatcher, like he's some kind of European folkloric troll. The guy's just doing his job, which in this case is making sure the kid isn't under the protection of a child-endangering idiot. Somehow, Arthur's the one we're supposed to be against?
The Movie From Arthur's Point Of View
Let's say we swap roles and the focus of the movie is on Brooks. Now we have an exciting adventure-thriller about a hefty man fighting for the livelihood of an innocent, corruptible child while remaining ridiculously chill and understanding the whole time. His only goal in the movie was to bail this kid out of the shithole life Adam Sandler was currently providing him (not bathing him, feeding him nothing but ketchup, providing him with deadly weapons, etc.). It's the tale of a man who has devoted his life to making sure abandoned children are raised in safe homes filled with love. Now that's a hero.
You want drama? How about pivotal scenes involving Arthur filing paperwork for a foster home for the boy? Maybe he makes a few phone calls to Sonny that go unanswered and we see Arthur's anguish; he just wants to find a decent home for a child that's just as deserving of love as anyone else. Maybe he and his wife can't have children of their own, so finding happy homes for children is the next-best thing. Why watch a story about a guy who doesn't want a kid when you can watch one about someone who wants to save a kid?