The PMI crowd generally believes that a project manager is supposed to manage uncertainty out of the project. The agile crowd tends to believe that uncertainty and change is something that should be embraced. Rather than managing OUT uncertainty, the agilist chooses to manage FOR uncertainty.
This difference fundamentally influences how we go about the business of planning projects… the artifacts we create… and how we interact with and manage our teams. The reality is that both worldviews have a place depending upon your context and problem domain. It’s up to us [as Project Managers] to recognize the nature of the projects we are working on and choose the strategy most likely yield a desirable outcome… for both our project stakeholders and our external customers.
We cannot check our brains at the door and blindly follow ANY methodology. It’s up to us to assess our situation and choose an approach that is suitable for the task at hand.