Does someone really need to play Harry in the Dresden Files Cooperative Card Game?
I'm the publisher. You CAN play without Harry's deck, but you run the risk of having an unsolvable board if you do. 

Harry's Talent has the ability to rearrange parts of the board in order to move things closer that need to be cleared before other parts of the scenario can be taken on. So on some boards you might not need that — random shuffle being what it is. On others, it's make-or-break. The reason why it's necessary to play Harry might not be in the rules (frankly it's not necessary to explain the why in the rules); the statement "Always include the Harry Dresden deck" however is.