We do it because slam-dancing is fun. Concert goers dance. Heavier music has heavier dancing. Slam-dancing has been around in many forms since the seventies. The only way slam-dancing will stop is if it's banned.
Parents think it is.
Teens do not agree. I personally think that in a responsible manner it is fine. There is no need for weapons at concerts. Leave your nightsticks, brass knuckles, and knives at home. These weapons do not belong at a concert.