That is a hazard - it's not a label that should be applied willy-nilly. On the other hand, if you leave the junk stat unlabeled, people will be deceived by the frequent exceptions.

(As for the aside: the trouble with BMI is that I'm not sure there's anything left once you take into account the other factors. I think it's a good rule of thumb for scaling human beings - increase height by ten percent, increase weight by twenty-one percent - but that's about it.)