When you tread water, you lift yourself up by pushing water down. Likewise, in any social hierarchy, people unsure of their own position will try to emphasize it by maltreating those they think rank below. I've read that this is why poor whites in the United States are the group most hostile to blacks.
"The surest way to work up a crusade in favor of some good cause is to promise people they will have a chance of maltreating someone. To be able to destroy with good conscience, to be able to behave badly and call your bad behavior "righteous indignation" this is the height of psychological luxury, the most delicious of moral treats."aldous huxley