Nothing!  It is what is wrong with Muslims. 

" ’Islam’ named not something that God gave to men, as is now widely imagined, but rather something that God asked them to give to Him—a quite different matter."

"the essential tragedy of the modern Islamic world is the degree to which Muslims, instead of giving their allegiance to God, have been giving it to something called Islam."

Wilfred Cantwell Smith

"I used to think that 'Islam' and 'Muslim' were one and the same, with the goal of all Muslims to be in (Islam); a state of engaged surrender to Allah: the One, the Originator of all things.  Following the publication of Qur'an and woman, I have seen that situations may arise where one might be forced to choose between the two.  To choose Muslim would mean a place for me and my children within the growing communities of Muslims worldwide.  It would mean peaceful greetings and warm embraces.  It would mean access to much needed support.  That it would not always mean surrender to Allah is a reality that I have had to accept with a great deal of regret. 

Amina Wadud