From the start of this game Destiny was meant to be a cooperative team experience. That's why it requires internet so you can interact with people you know to overcome the challenges the game presents. It requires you to have friends who own the game to be able to play with them however they also have these amazing forums and places where players can meet in order to play together if for some reason they couldn't form a team at any given time. I don't see why optional matchmaking couldn't be a thing but I guess Bungie will do whatever they see fit.