Ironically, this sort of nonsense invariably trains our adults to function as kids.
When you put it in those terms, you're right. Football, or other competitive sports, are only a part of what kids need to develop into functioning adults. They also need mental, scholastic, ethical and spiritual preparation to be worth a crap as adults.
But, sports teach valuable lessons that marching band, Boy Scouts and other activities just can't do as well. Most of all, on the playing field, I learned the lesson that life isn't fair. Whether it was the 108-22 loss on the basketball court when I was 12, or taking a back seat to the coach's son on the football team, I learned that no matter how unfair somethings are, you just have to deal with it, keep your head high, and drive on. Playing sports taught me how to work hard and give 100% in the face of adversity. It taught me that I wasn't the be-all-and-end-all, that I was part of a unit, working together to meet a goal. Yes, I even got hurt playing football and basketball...and those times taught me to recover and get back on the horse, so to speak.
Yes, sports are valuable, mentally, ethically and physically, to the development of kids. To deny kids the experience of playing on a team is to deny them valuable lessons and experiences that will help them throughout their lives.
Scouts Out! Cavalry Ho!