Your rationale has some validity, but by the same token, there's nothing wrong with encouraging children to give their best efforts in everything they do.
I do think there's something wrong with encouraging children to give their best efforts in everything they do. It's not realistic, nor healthy.
My DD just ran a 5K. She signed up 2 months ago. Giving it her best would've entailed running almost every day. Instead, she ran a couple of times a week and finished the race (without walking) in a mediocre 30 minutes. She ran with a friend, had a great time, bought the t-shirt, posted photos on facebook and now likes to run a mile or two for fun. I think it was one of the best things she's done in a while. And she didn't give it her best.
That's all I'm saying. I didn't say to heap praise on mediocrity. Just said that casual participation is underrated.