The value of the consultant (especially when playing an expert or collaborative role) is that he’s external to the organization, so he can see, say, and do things that others wouldn’t be able to.
To provide perspective, the consultant needs to be authentic. Otherwise, he will simply parrot back what the organization is expecting to hear.
This is why consultants have an expiration date: when you stick with an organization for too long, you develop tunnel vision, which hinders your ability to provide a useful perspective.