After reading some of the claims listed on the site you linked to, I can conclude that there is an element of misinformation behind the content. And because there is so much of it, it would be unfair to expect me to sift through the material and provide a rebuttal for each claim. So I will direct you to a book which, if you sincerely desire the truth, should answer your question: http://islamicbookstore.com/b7626.html
If the Qur'an has never been altered, what about all the claims that it has listed here: http://www.answering-islam.org/Quran/Text/
The Muslim Perspective
If God said "Thou shalt not kill" then why did he flood the whole world leaving only Noah and his family alive, and how is the destruction of Sodom justified (killing people for engaging in "immoral" sex), is God exempted from morality?
Why do bad things happen to good people?
Answers: Atheist, Christian, Muslim, Hindu
When did your religion or worldview first begin?
Answers: Christian, Atheist
Is Buddhism compatible with Christianity?
How do atheists explain the similarities between Christianity and Islam if they believe that there is no God?
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