Or perhaps there's a reason why we label ourselves? In the first place this has never shattered the community, alienated each specific group further from each other. Sure, we have arguments. Sure, the 'competitive' players might go to the 'casual' players and say that they're just complaining about things that kill them, or that they're just asking for things that would give them an edge. Sure, the casual crowd might go to the competitive gamers and say they should cool off, and that it doesn't 'really matter'.
Is it illogical, and misunderstood? Yes, of course. We're all "Fans" and there's no point in splitting it up. We've all taken a liking to Halo, enjoying the good's and acknowledging the bad's. But when we raise a point in our discussion, it always helps to be able to back it up not by cementing that 'we are more correct than you because we are X and you are Y', but by ensuring that they know 'this is the viewpoint of me, who is an X'. Sure, maybe we say it differently, but more often than not that will happen because there appears to be an ounce if idiocy involved within the point (E.g. "WHy does incin cannon kill me but not my teammates !???).
But differentiating the player base is both helpful in discussions, where you can make sure that everybody knows every different point of view possible. Why?
Because let's face it. There's always going to be a difference between the 'MLG' and the 'Casuals'. One side of them are players who hop on matchmaking just to have a blast. I have no idea how they do it but they can go around, get around 10 kills and 20 deaths, and still be "Having fun". Whether it's actual fun or if I'm wrong, I'm not sure, but they aren't going to be the "MLG" side of players who hop on to Arena, or Ranked, or try to bring up their CSR. These are the players who will, in pubs, consistently perform at the top of their pub lobby teams. These are the players who crave competition, who can feel boredom creeping up them in normal matchmaking now that there really isn't much point in playing, since they're going to do good, and the only thing that might happen is they absolutely demolish the other team - or he/she is put in a team full of noobs who still throw the game despite being carried. Casuals might ask for a buff to a gun - simply because they don't know how to use it - while Competitive players might be asking to nerf it because they've seen it used to it's full capability and it's absolutely devastating.
It doesn't matter where you are, or what you are, within a long-standing hobby there's going to be a split in the community someplace, somewhere. In gaming there are the 'casuals' who just play for 'teh funzies', the 'competitives' to like to win, who like a challenge. Maybe in Halo we also have the forgers, who might think that 343i should address the Halo 4 Forge ASAP, or the custom gamers, who think 343i failed miserably in custom game options.
This is for other games to. MOBA players have craaaazy competitiveness, considering it's a massive international tournament which gives you the largest $$$ prize in eSports, like, ever - but there's a "casual" crowd to. Call of Duty has some of the biggest eSports names and titles - heck, Cod is something you can participate in at this year's Summer X-Games, and will be broadcast on ESPN - but the casual crowd is SOOOOO MASSIVE.
Same with sports; the sports pyramid practically cuts it out into sections for you. Foundation, for the people who just start doing a sport, all the way up to Elite, people who are competing in Olympics and World cups and stuff. There's a "Casual" and "Competitive" crowd, and if we can discern it from the few hundred years of sports history, we should be able to know that - no matter what, a community is just gonna split up like that. You can't prevent it; you can say the wording is illogical and meaningless but you can't say the actual split in player base is. Calling the 'competitive' players 'MLG hardcore fans' and calling the casuals, well, 'casual fans' might be absolutely stupid wording once you take it literally, but you can't say that these different 'castes' are useless, because:
(tl;dr)
1. They each give a different point of view to the table
2. All together they're just one community anyway.