Red Team - Blue Team

As I was reading "Perfect Enough" there were a number of times the management consultants such as McKinsey & Company were mentioned.  I was wondering how often such consultancies offer recommendations against what the persons hiring them asked for.  In the case of Hewlett Packard McKinsey was hired to figure out how the Compaq merger would benefit them.  If the answer truly and honestly would have been "it won't"....would that message have been given to Hewlett Packard.

So, when hiring a consulting firm to give you strategic advice, wouldn't it make sense to hire both a blue team to research the pros, and a red team to research the cons?  Of course no one should really expect that all business decisions are made based purely on logic (look at how many companies move their HQ operations to someplace the CEO finds more attractive for their own personal reasons).