I guess to me nobody really cares about the self-defense applications of soccer or vollyball and if the sport aspect of Taekwondo is what you're into, that's great; enjoy it and do well.
It does seem though that at this board everyone seems to take MA so darn seriously and that if you don't train to use your art to defend you from armed biker gangs then you're not doing it right. So I think somone who *would* be interested in Taekwondo only as a sport would not feel very welcome, which is a shame because everyone fundamentally uses the same basic techniques so I think a lot could be learned all around.
Which is ironic because if by "MMA" you mean "UFC", "Pride", "K1", etc..., as many seem to, those are just sports as well, and it's hard to really take sword arts serioulsy as self-defense in today's society either. And so on. There are a lot of aspects and practices in MA today that are really just for sport but for some reason, sport-oriented Taekwondo seems to be looked down upon