The only people that dismiss the theory are devout believers. Their dismissal is based more on faith than science and scholarship.
Not necessarily. The content of the Pentateuch is the hardest to verify because it encompasses the longest time span but it's authorship is not impossible to determine. I hate to keep referring you to the above links I posted but the site's owner explains and answers the JEDP hypothesis in depth. Many supposed problems were shown not to even exist when consulting the original Hebrew.
Second, the Bible itself mentions that Deuteronomy was "found" centuries after Moses supposedly wrote the pentateuch.
How do you know this discovery was specifically Deuteronomy? It is described as "The book of the law." Well, the Jews refer to the entire Torah as "The Laws of Moses." Also, remember what had happened prior to the Babylonian captivity. The Israels hid many of temple artifacts in hidden subterranean cavities below the temple. This is why there is so much contention even today regarding the Temple Mount in Jerusalem and excavation. The Jews want to get down there and dig but the Muslims will not let them. Which leads us to...
Third, the bible describes Ezra as reiterating the Bible to the people. This reiteration had to be the publication of some redaction, canonization, or editing process of the bible.
Actually, it doesn't have to be like that at all. Remember the historical context. The Jews had just returned to Jerusalem after spending 70 years in Babylonian captivity. Because they were allowed to rebuild the temple the Babylonians destroyed 70 years earlier, Ezra helped the Jews get reacquainted with temple procedures and return to Jewish law after being under the authority of Babylonia.
It also shows that many of the returning Jews were the original captives who remembered the old temple and laws. It even mentions many of the Jews born in Babylonia during the captivity deciding to stay there instead of going all the way back to rebuild their ancestor's land. Their attitude was basically why should we leave just to rebuild a city that has no attachment to us? It seems silly to believe Ezra changed the system when the original captives could have exposed him immediately.
Finally, scholars look to differences in the language, grammar, and syntax of the bible. These differences suggest different portions of the bible were written at different times.
We definitely believe the Bible was written over the span of several centuries so I don't quite understand what you are implying. We also believe some books were possibly coauthored by more than one person (Psalms, for instance). Also, the syntax sometimes changes in one book (Isaiah, for instance) because he wrote his book over the course of his lifetime and not all in one sitting. Some believe Daniel did the same thing. This makes perfect sense. Look at the writings of secular historians. They were a single person but looking at their histories will also reveal a switch of style, temperament, and syntax.
