As someone who knows absolutely nobody else in real life that plays Destiny I'm more concerned with the lack of social functions in the game that make it really hard to meet people to play with (hence joining the clan, hey guys). For shits and giggles though I can't see any problem with allowing groups bigger than 3 since the only time that would be a balance issue is in strikes or 3v3 crucible which wouldn't let you all in anyways.