Johann Hari (for once) has a pretty good piece here about the great management consulting scam.
But for all that, I think that he's wrong to blame people for taking an opportunity. I spent a large portion of my life doing technical consulting and the higher up the food chain I moved, the more I found insecurity about what needed to be done. When I was consulting at the bottom of the food chain, I was generally doing some clever stuff that their staff didn't know how to do.
As I started "engaging" higher up the food chain, I found myself spending more and more time rubber-stamping the opinions of techies on the ground who a) knew the problems better and more completely than I could ever manage and b) knew perfectly well how to fix the fucking problem. The real problem is that the management, for whatever reason, are wildly insecure about the solutions proposed by their staff.
Equally, I find that very often people are quite happy to pay for my time and then not execute the advice I give them, possibly for quite valid reasons, but reasons they don't share with me.
So yeah, be pissed of with consultants for taking the piss, but really the blame lies with the insecure management of the company or government department who need the "impartial blessing" of a third-party shaman before they dare to do anything.
It's the uselessness of the people running the show that is really to blame, along with the "cover your arse" nature of government and corporates.