I just had a thought.
@DaveB is suggesting that MMA is a sport, and so cannot be a martial art. The two are mutually exclusive. It's true that a dog will never be a cat, even though both animals might crap on your floor. They might both be floor crappers, but a shitzu will never be a calico. In the same way, MMA, as a sport, just is a different thing. Is that true, DaveB? I'm sincerely not trying to put words in your mouth, but to sum up.
If this is somewhat true, my confusion, and maybe some other people, is that this is independent of application. If sport and martial art are different creatures, this would be true regardless of application. A sport that is trained and used for self defense would not be a martial art because it is a sport. Period. Trying to justify your perspective beyond this just muddies the waters.
@gpseymour suggests that a style can be both a sport and a martial art. That the two are not mutually exclusive. He's not too worried about distinguishing between a sport or a martial art. For him, the key is application, which as I explained above, is really irrelevant to DaveB. So, a dog that craps on the floor or a cat that craps on the floor. The salient point is that they are both crapping on the floor. And the end result, even though both are coming at it from different directions, is a stinky room.
@DaveB I said before, I think you're a smart dude, but I predict that your perspective will soften over time. You have some interesting ideas that I appreciate. The reality, though, is that martial arts styles are both too inbred and also too diverse to make it easy to apply binary reasoning to them. They are not all one thing or another. Usually, they're some combination of both.