There is no competition in Aikido. Despite this maxim, it is still hard for people to accept. Competition itself is not bad, but what it brings out in us can be detrimental. It can be harmful because it has a detrimental affect on the ego. Let's think about the game of golf. Golf is fun. Golf is social and the experience can actually be heightened when others play it with you. There is technically no winning or losing in golf since it is a personal pursuit where the golfer is trying to improve upon a skill. There is also no such thing as a "perfect" game - nobody ever shoots a 0. Given that golf is a personal pursuit it can actually make someone a better person because they have to conform to a set of rules which penalizes them if they break them.
However somewhere along the line, golfing became more about winning by beating others than as a means of personal development or sportsmanship. This has brought about such unsavory things like cheating, performance enhancing drugs and bad behavior. In a 2002 survey of America's top 400 top business executives who play golf, 82% admitted to cheating. In a 2011 poll, 54% of the PGA tour caddies said they had witness some form of cheating. Today with sponsorships and praise, we only care who won or who was the best and we rarely care who is the better person.
This could happen to Aikido also if there was some form of competition. What would dojos be like if there was a competition for prize money and sponsorships? How far would people go to "sell" the competition by speaking disrespectfully about their opponents? What would people be willing to do or more importantly forgo in order to win? The answer is that Aikido would then go the way of every other martial art where the emphasis is on who has the best abs.
Aikido is a do or way and like golf it is a singular journey where the only competition we have is with ourselves. If we are not training for ourselves, we are training for our egos or more importantly other things and other people. Our ego wants praise, accolades, fame and fortune - everything that exists outside of ourselves. This "win at any cost" perspective is one of the negative sides of competition and thus why there is no competition in Aikido. This is why O Sensei said, "Masakatsu, Agatsu" or that the real victory is the one over yourself.