In the movie it was portrayed more as an act of hatred of lower class. In real life, that was done at first, to preserve order for a small amount of time so they could prepare the boats and figure out a game plan. Once panick started to take hold, it's sad, but they were simply forgotten about. The men up top who gave out orders got preoccupied with other things, which I think is understandable, and the men below were simply waiting for the order which never came. They were trained to do only what was ordered of them, so to be truthful, they thought they were doing things exactly by the book.