Sanists vs Insanists

Has everyone seen Shutter Island?  There seems to be a fierce debate over whether or not Leo's character was sane or insane.  The fiercest part is coming from the insanists.  Their main claim is how the book was written, and all the coincidences of the names.  I have to ask why does this all matter.  Why can't a film be ambiguous to these people, why can't both theories have great points to their credit?  Why does a movie have to be one way or another, isn't that the point of movies for the most part, each person sees the story they want to see?  True, there are some films that go full fledged dark water where there is no discernible story or thought put into certain direction (see Eraserhead) they let everything up to the viewer and it becomes a big hangover mess, but when done with a plan ambiguous themes and endings can make a film exponentially better.  You just can't be around fascists. 

I could see how both endings could work, but I'm leaning more towards that he was sane the whole time.  You have the mysterious notes, meeting the girl in the cave, his access to all over the island which leads to the fact of why would they go through all of this trouble for one patient.  They are going to put on a huge performance thereby neglecting a good majority of other patients during this time possibly sending them into deeper psychosis.  I don't think so.  Not too mention it is too easy for a movie to just be that story where the guy is really insane the whole time, do you want him to wake up from a dream too?  The insanists look to the case of the book, I didn't know you could watch a book.  I look at the director, for anyone who has seen King of Comedy know that this guy is pretty good at ambiguity as well.

But what if it is neither?  What if it is both.  What if it is a story of him over a longer period of time than he thinks and he really is going insane slowly.  He is insane but he is correct insane, kind of like that whole broken clock thing. 

What if his partner is fake and never existed?

Who knew Leo would be in two of the most debated movies of the year.