I can see being skeptical of the JD/MBA because both programs are shortened in most cases. But if one has an MBA and decides to get a JD, or vice versa, I think it can only be viewed as a good thing.
Also, we hardly ever hear any criticism of JD/MA or JD/PhD programs. Wouldn't these people be just as "indecisive" as a JD/MBA? Maybe it's just because the JD/MBA is the most common joint degree program....