Personally, I think the analogy with boxing is a good one. Boxing doesn't allow kicks; does that mean that learning boxing is irrelevant to learning self-defense? I wouldn't think so. I would think somebody who trains in boxing can probably defend themselves better than somebody who doesn't train in anything at all. Likewise, somebody who trains in sport taekwondo can probably defend themselves better than somebody who doesn't train in anything at all.
So then, it seems to me, the question becomes this: as you go around looking at martial arts, trying to decide which one to study, are you going to just pick the one that's best for self-defense? If so, that's fine, but there are other reasons to study martial arts too (sport, exercise, recreation, hobby, family activity, etc.)
That's easy. I don't think anybody will argue against me on this.
The best self defense is either Chic-Chic-POW or, possibly, Ameri Do Te.