1) The discussion is really about ANY sport/league that would have this policy.
2) Have you been active in young (4-9yo) child sports? The kids might not be misbehaving, but they might simply not want to listen to the coaches, not be paying attention, etc. I was helping coach DD's 10U rec softball game one year. We had 3-4 stations going where the girls were working on skills. One was hitting a ball off a tee. One girl walked right through the middle of the drill just as another girl swung... she got a line drive in the side of her head.
3) Around here, coaches don't have the power to kick kids off the team (again, talking rec). It doesn't matter if Johnny misses every practice, the rules still require the coach to play Johnny for 1/2 the game.
1) Er, OP was talking about "U12 soccer", and THAT is what I was responding to. Let me restate:
"I'm glad my kids aren't in a sport where I have to attend all the practices. What a waste of time."
2) I thought U12 soccer was for age 11, not 4 to 9.
My daughter active in dance between about 4 and 9 (and son between 4 and 6). It's not the same atmosphere as most sports, but I'd still call it a sport (group of kids practicing together with one teacher). Not only did I expect my child to behave, but also to listen. Parents were allowed to wait outside the dance studio, but we weren't allowed inside the studio to watch.
My son was in taekwondo from about 6 to 9 and again was expected to behave, listen, and pay attention, but there is no way the teacher would ever allow a parent to scold his or her kid during practice. My son was in football at 9. Again, he was expected to listen and behave. Parents could come to practices (which were 2 hours, 5 days a week), but weren't required.
If the problem isn't misbehaving but rather not listening, that's the coach's problem during practice, and my problem
after practice. Going up to my child in the middle of practice to scold him or her for not paying attention or following directions undermines the authority of the coach. It would be like going to Kindergarten and doing the same thing in front of the teacher.
Although the more I think about it, of my three examples, the first two were paid professionals, so that changes things a bit, I guess.
Assuming, at this point, I had another child, and that child, at the age of 4, decided to join a sport, I would show up for at least the first few practices to make sure the coach wasn't a creeper and that my child got along with the other students, followed directions, etc., but I would most likely NOT attend every single practice, and would balk at signing up for any group that required so.
3) I don't know what the rules were in my son's football team, but if this is true, then policy should be changed to allow for children who are behavior problems to be removed.