Again, that's a black and white view of things, and violates the live and let live golden rule. Not just now, right after the death of the prophet Islam began to diverge. The Quran, itself was assembled into a book, after his death, during the 1st or 2nd caliphs time.
You should read up on Islamic history. The general populace has had several ebbs and highs in the nature and intensity of their belief, based on context and time.
Islamic history also has had a lot of free thinkers, even in medieval times like Al Ma'aari[1] and Ibn Rushd[2]. I also learnt, that there were liberal Muslims in 15th century Andulus-Spain, from a fascinating book by Tariq Ali[3].
I also read this recent article on 'free thinkers in Islam'[4]
Not sure if you know, the Turkish nobel prize winning author, Orhan Pamuk, also identifies himself as a cultural Muslim.
So you can't wish away the diversity and free thought. Currently we seem to be going through a phase of high tide in intensity of belief. You may be surprised to see it ebbing away in the coming decades. Just my view.
[1] https://en.wikipedia.org/wiki/Al-Ma%CA%BFarri
[2] https://en.wikipedia.org/wiki/Averroes
[3] https://en.wikipedia.org/wiki/Shadows_of_the_Pomegranate_Tre...
[4] http://www.independent.co.uk/voices/commentators/islamic-his...