I agree with what most have said here.
Because a player doesn't show his emotions does not mean he cares any less than a kid who does show his emotions.
IMO if a player lets his frustrations known to a fellow teammate over errors or lack of caring (in his eyes) he will quickly become irrelevant as far as a leadership role goes. He will accomplish the exact opposite of what he thinks he is doing. ie leading. He will be labeled a bad teammate and selfish player.
Would your son want a kid who makes an error to jump up and down and stomp his feet to let others know he is upset with himself? I don't think so.
Players, in any sport, have different ways of preparing for and playing games, and handling adversity. Because someone is laughing or joking before a big game does not mean he is uninterested, less passionate or not ready for the game. I think I'd rather have the guy who is loose and having fun playing a sport he loves.