It's an MMO. do u have any idea how many serious MMOs have dance emotes? look at it this way, even with the apocalypse happening people need to take time to rest, return to base, and unwind. many people do this by dancing and partying. It's kind of symbolic really. People party and slack off (and play videogames) even at military bases. as for people dancing in the cosmodrome or the crucible. you can't stop gamers from fooling around. if they can't dance they will teabag, melee their teammates....etc.