There's also nothing in the books about how Harry is a serial killer - slicing people open between cases. Just because we haven't read anything about it happening doesn't mean that it hasn't happened - absence knowledge about those killing is not conclusive evidence of impossibility of them happening.
Personally, I don't think Dresden is a serial killer - but since most of the stories are his point of view we'd never know unless he told us - or unless we look at what we have and draw conclusions.
The Knights of the Cross have been battling those beings for 2000 years. Admittedly their records have taken several hits, but they only know of one way to remove a Shadow - and by 'they' I'm including the former host/current knight. Dresden couldn't figure out how to contain the thing inside his head - it kept talking to his subconscious. Bob couldn't even get started on a way to remove the Shadow from Dresden's head.
That's both Bob and Harry not being able to get rid of the Shadow because it is part of Harry.
The way I see it - there is only one logical way to drive out a shadow from another person:
Break open the gates of hell to release the Fallen into the world. With the full power of the Fallen walking the Earth the shadow wouldn't be inside anyone's head.
Other than that, the setting as written doesn't support it - for the same reason that Micheal didn't have Dresden\s back when they met Lea in the Nevernever that first time. Correct me if I'm wrong but the setting is all about freewill. Did you decide to kill someone with magic? Then you're a lawbreaker even if that person deserved to die. Did you make a deal with the Fairies? Then the forces of Heaven WON'T help you. Not "can't" but "won't". The conversations with Jake make it clear that the forces of Heaven aren't there to save mortal from their mistakes - because if they did that then mortal choice wouldn't matter.
If you take an action that results in a Fallen casting a Shadow inside your head, you did it. You might not have had all the info, but you made a bad choice and even someone like Jake won't drive the thing out.
Think about the problem of restoring a Renfield. If the books hadn't explicitly said it was impossible people would be asking how many shifts to fix that. If Harry hadn't have taken a year working on a spell and failing (how many shifts could a wizard gather in a year??) then people would say "enough to take Susan out and then enough to take out the infection - say 30 shifts?" when talking about curing Red Court Infection. Well, Dresden worked for years, on and off, to drive a Shadow out of his head and he failed. His own head (where he had home field advantage), not someone else's head (he might have to break a law of magic to get into someone else's head to find the Shadow). Dresden, who better at the spell work than he is at blasting and one of the top 100 wizards alive, couldn't do it for himself.
That leads me to think that it's one of those impossible things. If you have evidence from a book that I'm wrong I'll be happy to hear it, but just saying "absence of previous known success is not conclusive evidence of impossibility" will just get me back to talking about the pile of heads that Dresden collected as he stalked the night looking for victims.
Richard
