I have played several different sports, and honestly I would have been heartbroken if my parents couldn't come. It was one of the few times they actually acted proud of me (yes, that may be a whole different problem, but).
My father got a yellow card at a soccer game once for cursing at the coach. Then again, my coach one year got kicked out of the game for threatening the referee. My mom kept a close reign on my dad at the games after that, and the coach calmed down. For the most part, parents just come cheer on their kids, and though sometimes a few of them get out of hand, that is their problem and they shouldn't ruin it for everyone. I do think people should be banned from coming, just like fans are banned from sports events for doing similar things, but parents coming to the games is a pretty important part of life in suburbia.
I do agree that the focus should be on having fun, enjoying the outdoors, and what have you, and not on winning. I've had coaches in various sports that were so focused on winning they flipped out all the time, and coaches in various sports who put everyone in for equal time, in all the positions, because they wanted everyone to have fun and nobody to sit on the sidelines the whole game.
Kids should play sports. If you want to avoid the craziness of the team sport competition, have them try gymnastics or swimming or tennis or golf instead of football and soccer. I never broke anyone's bones in my years on swim team, but I broke an ankle and a nose playing soccer (other people's).