I guess my problem with it in kids and youths as the poster was talking about is the fact that its a very, very, very thin line between show boating and "playing your best" against a weaker opponent.
As you're older, its easier to understand the difference there. When you're younger though, its hard to grasp it.
Not everyone is a Barry Sanders, who could break off a 80 yard run breaking 6 tackles only to reach the end zone for the 3rd time in the day and immedietely go hand the ball to the Ref and head back to the bench like it is no big deal.
I think there is a lesson to be had with teaching kids a bit of humility, reservedness, and restraint when they're younger as those are what helps create an athlete that is not a show boater. Whose not going and putting on faux Hall of Fame Jersey's or throwing popcorn into their face.
Telling your super star youth players to go out there against competition so far below them that its uncanny and telling them to go all out just kind of pushes the notion that humiliting and taking advantage of the opponent isn't just okay, its expected and good, and if that's okay then really what's wrong with taunting or smack talking an opponent when its basically doing the same?
That'd be part of my issue with youth (again, with keeping starters in there and telling them to "go all out"). You talk about the "lessons" the other team needs to learn, but what lessons is that teaching to the plays that are doing the winning.