First, my understanding is that the term "consultant" has become so broad that it basically just means "contractor" for intellectual jobs; it covers coding, management, business strategy, and a million other things.
Second, even if we stick to a slightly more narrow definition, consulting essentially boils down to smart people going around to existing businesses and telling them how to do their jobs better (hopefully). (Presumably, these businesses don't need the smart people most of the time, which is why they don't have them as employees.) At least superficially, this seems like an appropriate use of smart people: target them at the problems where they are needed, which are dispersed across many businesses.
Now, if finance and consulting are actually sectors that aren't contributing to society (a net drain), then there's a real problem. But if so, the fact that so many smart people are going into them to make money is just the symptom, not the problem,