I'm not sure which is more concerning - That someone had to create a list for how to talk to a coach. Or that people are arguing about it.
I am pretty sure that when a player leaves a team because of "coaching" - it's because that coach is a horrible communicator. Coaches using a team manager has a mouthpiece/proxy is weak. We are coaching kids, not the Lakers. This standoff approach to dealing with parents is ridiculous. Engage them. Let them know your philosophy / plan for the season. Talk to them about what you will be training. Talk to them about various systems of play that you might use. If your team has a crappy game, acknowledge some of the reasons why. If your team has an amazing game, talk about some of the reasons why. If a kid has a great game, text the parents and tell them specifically what you liked about their performance that day. If a kid has a horrible game, reach out and discuss what they can do to make up for it.
Most soccer parents are pretty clueless about the nuances of soccer. They see a "big kick" as a sign of a good player. Or that their super fast kid with the touch of a donkey should get more playing time than the slower kid who makes the right decision with the ball every time.
If as a parent, you are mad or have a question about something, you have every right to ask the coach about it. But probably not immediately after the game has ended. And certainly not while the game is being played. Unless it is a safety issue, the 24 hour rule is a good one to follow. Sleep on it. Shoot your coach a note and ask for a meeting. Buy him a cup of coffee or a beer.
But ask your kid about it first. You'd be surprised what kids have to say.
Examples:
Dad: "How come you only played 5 minutes in the 2nd half?
Kid: "I told the coach that I was about to throw up and I didn't feel well. He kept asking me if I was ready to go in. I didn't want to barf all over the field."
Mom: "Your coach needs to make sure that you are playing striker all the time. Doesn't he realize how good you are?"
Kid "Coach pulled me aside yesterday and told me that he thinks I am one of the top 5 players in this age group. He said he wants me to try other positions because if I ever move to a new team, it will be better for me to be versatile. He said that he knows that I can score goals, but wants me to read the game from different positions."
Dad: "How come you played goal keeper? That's not your position."
Kid: "It was my turn. We rotate for now. And the girl who was supposed to play in goal, had a really sore wrist from a gymnastics meet she had yesterday. I volunteered to play in goal. It's kinda fun!"
Of course, there are just some jackass coaches out there that probably require your intervention:
Dad: "You played great. Why did you come off of the field crying at halftime?"
Kid: "Coach told me that if I didn't slide tackle #12, then I would sit the bench in the 2nd half. I was afraid to get a red card again, so I didn't do it."
Mom: "Why aren't you eating your lunch?"
Kid: "Coach told me I am too slow and that I need to lose weight if I want to be faster"