Rashadi, thank you for the insightful post.
The sole reason I believe that all of the books have been tampered with is simply this: They have been in the hands of men, and have been since they were first ascribed. Did Muhammad, who was said to be illiterate and unable to write, write the Qur'an himself, or did he have someone do it for him? If yes, then that is a point in my mind for weakness right there. If not, remember, the book has been in the hands of men for 1400 years. There is always room for something to go awry.
You say that the work is protected by Allah himself: If that was so, why were not the preceding books? I am told the Qur'an is a "fixed version" of the Jewish Torah. Why was the Torah not in Allah's care? Do you see where my line of thinking comes from?
In the end - and yes, this is my personal opinion and should in no way be seen as trying to discourage those of you mighty in your faith to believe otherwise - that I cannot be certain than this book is uncorruptable. Even if there is a consistency to it agreed upon by Western scholars, there's just a great leap of faith, in my humble opinion, to hedge it all on this. Consistency doesn't necessarily mean infallibility.
I am almost inclined to mention someone - who I believe claimed to be Muslim - that argued against the 100% validity of the Qur'an, but I will not mention him here because it's controversial and I don't want this thread to crumble into a flame war.
Oh, and thank you all for your insightful posts.
No problem, brother/sister, no offense taken at all. I can not convince you that that the Quran is the word of Allah because this is between you and God but what I can prove is that it is not altered, changed or deleted. This has been well proven by scholars, historians and authors who have written about it a great deal. The Quran has been in the hands of people since day one but the it is not only a written text but it is oral as well. Quran means "recitation" and it is something that is to be recited and this itself is a proof alone but there is more. The University of Munich conducted a study on this subject and they gathered over 40,000 complete and partial copies of the Quran from all parts of the Islamic world and from the earliest to the latest ones, after years of research, they confirmed and found no difference among them. There were no different versions or texts.
Unfortunately, the university was hit during ww2 but they confirmed the fact that the Quran has been preserved since day one. It is not for me to convince you that the Quran is the word of God because you have to do that on your own but what I can do is prove that it is not altered, corrupt, changed, deleted, etc. As for the person who you mentioned who argued against the Quran, I love to hear more about him and I have a feeling I already know who it is but I still like to know for certain but even he will have no real argument against it. The Quran was already in the memory of thousands of the companions and early followers of the Prophet(saaws). This tradition has been passed down to this day and today the number is in the millions. One can take all of the Quran's and hide them and it will be brought back the same day word for word because it is in the minds and hearts of millions.
I respect your opinion and I am in no way trying to attack you or force you to accept it but I could give you an advise and just keep an open mind, pray to god for guidance, ask Him to guide you to the truth, and research the Quran if you are interested. If not, it is your choice my friend.
As for the previous revelations, they were meant for a temporary time for the certain people. For example, the Torah was revealed to Moses(pbuh) and the Injeel was revealed to Jesus(pbuh) and these were valid revelations from the same Almighty God and we believe in them. God did not forget about them but He simply sent His final scripture for all mankind and for all times, and it is a confirmation of what went before it. What we have today as the Old Testament and New testament is not the actual Torah or Injeel as given to the prophets but it is a corruption with some truths in them. My claim is that these books were never the originals from the start but corrupt manuscripts written by later unknown authors. Of course Allah(swt) could have protected the previous scriptures and He did do so because His original words will always remain but they weren't for all times. In the Quran, God tells is what basically was in those books and the Torah was a scripture which contained laws for the Children of Israel and their religion was Islam (Submission to God). The same way with Jesus(pbuh), when he came, his duty was to coinfirm and uphold the Torah, call his people back to the straight path and the Injeel was in harmony and was a confirmation of the Torah.
The majority of the Jews rejected Jesus and did not do as they were commanded to do by God and by Jesus. Then, He finally sent Muhammad(pbuh) and revealed the Quran to him which confirms the previous messages and is for all of mankind. So of course God could have preserved the previous scriptures and who knows maybe there are still copies hidden somewhere and if not, He has sent the Quran for all times and it is sufficient. So my dear friend, I hope you are not offended by anything and don't take me as trying to convert you because only Allah guides and this is between you and Him, but I am more than happy to help in anyways explain your questions or comment on any issues you may have. May God guide you and everyone, Amin.