Competition provides an opportunity for one to succeed. Competition promotes hierarchical distinctions. Competition breeds insecurity. Competition undermines one's confidence and self-esteem. Competition makes one afraid to take risks and try new ideas that might not work.
Competition undermines trust and mutual relationship.
Competition encourages those with power to use that power to maintain their position or advantage at others' expense. If I don't compete, others will get opportunities that I won't. Sometimes I compete because that's the only way people seem to relate around here. I like being the best. I don't like to admit it.