It's just like a BBQ... everyone has their own opinion on how to cook the meat.
Regarding convincing the parents and coaches, I've found in the engineering field that it's extremely hard to convince someone in authority to change their approach when the current method seems to be working. In the case of the weight room, "working" to the person in authority == sweaty/sore kids. It's rare for someone to want to make a decision and take an informed risk... they would rather stick with the status quo (after all, other people do it this way). My solution has always been to sell an idea through fear, e.g. "company X or product Y is going to beat us because they are doing things better and we need to change". A similar approach could be used on parents and coaches.
- Your kid squatting 405 has a better chance of making the team than if he squats 225, especially if he's competing against other kids who are lifting similar weights
- Team XYZ has kids squatting 275#... we need to squat more weight if we want to beat them
The argument of "hey, we'll be better if we add 100# to everyone's squats" is going to be a tough sell... even though we treat it as common sense on this board.