I know that often times, developers and gamers alike don't really care what the rating on a game is, but from what I've heard (all speculation of course), is that Bungie is aiming for a "T" rating for Destiny.
If this is the case, which I hope it isn't, it will be a huge mistake. The story for what Destiny is claiming to be, cannot be done justice if Bungie doesn't allow for the grit, violence, language, etc that would come with that setting, it can't be believable.
If the world is almost completely wiped out, and the human race is having to fight several other species in a last ditch effort to survive, you better bet that there will be "F bombs" dropped, there will be people being shot (meaning decent amounts of blood), etc.
Bungie, please, don't let yourselves be held back by a rating in order to get more sales. Make this game an "M" rated game. Anything less would be simply uncompelling and unbelievable, and would really detract from the story and mood that would be present should this situation in this game ever really happen.