I think there is a big difference between a child learning to lose and learning to be a good sport in accepting a loss. My second grade girl lost in basketball this weekend and did not want to go and shake her opponents' hands in the line that forms after the game. I calmly told her if she wanted to play next week she needed to go and shake their hands in a good sports way. She did.
I don't want my son to like losing. But when he does lose, I expect him to respectfully look his opponent in the eye, congratulate his opponent and shake the winning wrestler's hand and then do the same to both set of coaches. After he has had some time to handle a defeat, I want him to think about what he can do to improve. I would not hesitate to pull him from a meet the following week either if this became a problem with him.