Just because there are some ancient "holy texts" (in each religion) doesn't mean that people will follow them.
This is true. It's the difference between 'religion' and 'tradition.' I think it well to distinguish between the two.
The tradition of Islam, like any deep historical tradition, is filled with triumphs and atrocities. The Golden Age of Islam brought us amazing advances in mathematics, biology, physics, and justice; not to mention the stewardship of the knowledge and philosophy of ancient Greece. Adherance to the Qu'ran, as a book of literal truths, has brought us Sharia law, xenophobia, and holy war ('Jihad'), among other things.
The religion of Islam, however, requires one to follow the holy texts, as they are the primary source and justification of the metaphysics behind the religion.
The difference is both simple, and deep: it's the difference between terms such as 'Arabian' and 'Mohammedian.' It's not just Islam, either: this same difference between tradition (culture) and religion (metaphysical foundation) is found in Judaism, Christianity, Taoism, Confucianism, Mithraism, etc. Essentially, in every religion (of which I'm cognizant) which relies on a book or set of books claimed to hold a Divine or Holy truth.
Christian example of the difference: Presbyterians as contrasted by the Westboro Baptist Church.
Happily, the history of humanity seems to point toward our ability to do what's right, at the expense of doing what's holy - regardless of the set of metaphysical laws into which we're born and raised.
