Dominance and submission are not unique to BDSM, it is deeply wired in our psychology as a species. Hierarchy is a natural human phenomenon. We are status-oriented, competitive, and we seek to feel important than and superior to others. No matter how many times we uphold the myth of "freedom and equality", we live in a world of social stratification, rich and poor, ruler and ruled whereby the majority submit to the will of the minority. Hierarchical structures exist in almost every organization -- military, government, corporations, religion, sports teams, families, etc. This alpha-omega model is necessary for us to live cooperatively (Thomas Hobbes asserted that it helps to promote internal order within communities), to make decisions so that it can be carried out efficiently, to ensure the survival of the group for the next generation.  This primordial ranking behavior has defined us since the dawn of our race. The ubiquity of dominance and submission in our world is often seen in the form of competition. Charles Darwin noted that we are competitive over food, and, more importantly, over sex. One of the purposes of establishing hierarchy is so that those who land at the top of the pecking order will gain the sexual favors of the opposite sex, typically between males for access to females. Coming out ahead is a display of one's genetic endowments, AKA ideal sperm donor. Yesterday's muscles and hunting skills are replaced by today's cars and bank accounts. People need to know where they stand and who has the power, who is the best, who has the most resources. In other words, who is superior and who is inferior, who gets to mate (and live), and whose genes must die with the generation.