While the title, the three laws and the names of some characters are the same as Asimov's stories, the plot and most of the assumptions of the movie do not follow closely Asimov's novels so I don't think you'll find any real coherence in the movie.
In short, out of universe, the movie would have lack any interest if it were to develop as you suggest. In universe it's assumed that VIKI is "powerful" enough to disrupt any direct attempts to kill her via direct action so that the presence of a human is necessary for Sonny to actually understand why VIKI's logic is flawed. Through its continuous relationship with a human, Sonny's able to develop a better understanding of what humans really want (i.e liberty over being ruled for their own good) and that allows him to actually rebel against VIKI instead of following through like the rest of NS5 models.
This is just a personal opinion but the I Robot movie tries to mix without success several Asimov stories resulting on a confusing story at best, specifically if you haven't read the books. Stories present go from a lost robot, where we see Sonny get "lost" among a lot of other NS5 or VIKI being inspired by the Machines short stories. Additionally I think the whole plot is inspired on the invention of the law Zero by R. Daneel and by that character in particular.
However, in the novels Asimov takes the time to explore all the complexities and philosophical intricacies of the three laws and what motivates robots to act the way they do. In fact, all of the stories are based on exploiting that fact to make you realize that, in the end, the robot couldn't have acted any other way... Due to the presence of the three laws.