Sure, there were movies before there was sound. Those Charlie Chaplin silent ones. Never seen them. No clue what they're like. But music adds so much depth, and so much texture to a movie, that I could hardly fathom a movie without it. I mean, what is Casablanca without "A kiss is but at kiss"? Sure, great screen chemistry, et cetera. But the song, think of the song, and the scene just floats right into your mind, easy as can be. And the point is, that movie would not be that movie without that song. If there were a different song, or no song at all, then it would not be Casablanca anymore. It would be some sort of weird mutant.
Music brings movies to life. You can have all the dialogue you want, without music, it's gonna be a boring movie. Look at thriller/horror movies. They rely very heavily on music. Or sound effects at least. If you turn off the sound while watching a horror movie, you get mildly uncomfortable maybe. Nothing serious. But if you turn up the sound, and you don't even have to watch it. Although the movie really is the interaction between the picture and the sound. But even if you just listen to it, goosebumps, baby. And if you listen and watch at the same time, get ready to wipe your pee off the floor. Horror movies are the most obvious example of where they use sound to great advantage. However, this is done in almost all movies. When was the last time you saw a movie which had no music? You probably don't remember. Music is a great tool for creating atmosphere. It is also a relentless tool for emotional response. You can shut out the picture, but you can't shut out the music. Music is so versatile that a few bars of Unchained Melody can evoke a response that it would take watching Ghost for an hour to replicate. All in all, I haven't argued my point very well, I admit, but I think that you'll be hard pressed to deny it.