I'm often suprised with how dogmatic some people can be when it comes to fundamental ideals. Shades of grey are often taken and merged into one consistent strain from which all enemies of the faith are attacked.
Such seems to be applicable to both the theories of Prof. James Kugel and his detractors.
Prof. James Kugel is a professor at Bar Ilan University who has made a career out of "proving" that the Bible is the product of multiple authors. He is extremely educated and well-published on multiple subjects. In this idea, called the "Documentary Hypothesis" he is both right and wrong.
He is right to assert that there are multiple authors to many books of the Bible from Yehoshua on. In many cases, he can even bring support from the text as well as statements by Chazal. How many times does the phrase "until this day" appear in earlier books of the Bible? And how many times does the event described by the phrase cease to be applicable later on as history moves forward and circumstances change? For example:
"But the Yevusi, the inhabitants of Yerushalayim, the children of Yehudah were not able to drive out; and the Yevusi dwelled among the children of Yehudah, in Yerushalaym, until this day." (Yehoshua 15:63)
Clearly this chapter was written by someone who lived before the conquest of Yerushalayim by Dovid HaMelech, a"h. The amount of kri and ksiv portions is far greater than in the Torah. Many more examples are littered throughout the Tanach and there is much debate in certain parts of the gemara (see the beginning of Bava Basra, for example) as to who wrote what and certain characters (eg. Iyov) even existed. In other places, the Gemara will even given further proof to the editing process the Nach portion of Tanach went through by quoting verses that cannot be found in any modern Bible.
Even the authorship of the Tehillim is clearly that of multiple authors. While it is beyond doubt that all were inspired by ruach hakodesh, the title lines of many prove multiple authorship while the content of others (eg. 126, 137) were clearly written by later nevi'im.
But it's quite different when it comes to the Torah. For one thing, it is not a principle of faith to believe in Divine authorship of the Navi and Kesuvim parts of the Tanach. These were clearly the works of human beings inspired by ruach hakodesh but not the direction, unfiltered dictation of God to Man like the Torah was. Chazal allude to this by noting that the difference between Moshe's prophecy and later ones was that Moshe saw things through a clear lens while the later nevi'im saw them through a distorted one.
The Torah is intrinsically different from the rest of the Tanach for this reason. It is the clear, pure word of Hashem Himself, a result of dictation from the Master of the Universe to Moshe Rabeinu, a"h. The version we have in our hands today, with only minor exceptions, is the same text that was handed to Moshe at Har Sinai so many millenia ago.
Ah, but the Documentary types will point out contradictions, typos and other "mistakes" that they say prove the Torah was also written by multiple people and not by God. Like rumours of Elvis being alive, the existence of the sasquatch, and Ponzi schemes, biblical criticism raises its ugly, scholarly head every so often to regurgitate yet another set of "proofs" to show that the Torah is not Divine, chas v'shalom.
This form of academic kefira has been going on since the 19th century and has been repeatedly shot down by talmidei chachamim with equivalent training in scholarly methods. From Rav J.H. Hertz to Rav Dovid Tzi Hoffmann, flaws in the Documentary Hypothesis have been exposed through which a Mac truck could be driven.
Naturally, this hasn't stopped these dedicated "scholars". The primary gain from proving the Torah is just a human document, and a shoddily written one at that, is too great to let facts get in the way. For most, it is a chance to remove the burden of objective morality, of an external understanding of right and wrong, from their lives so they can justify their personal lusts and amibitions. For others, like Professor Kugel, there is probably a sense of intellectual honesty. He cannot, having read so much, believe the Torah is true and does not want to lie about it to himself or others.
What does distinguish Prof. Kugel, however, is his insistence that the main difference between the Torah and other contemporary documents is its insistence on morality. He is able to bring many examples of stories in the Bible that are similar to the myths of other people but also points out that the Jewish version of the story is meant not to simply relate history but also impart a moral lesson.
The problem with this approach comes from something Chazal says - one who breaches a fence will be bitten by a snake. The authority of our holy Torah comes from its Divine origin. As God's revealed will written down faithfully by Moshe Rabeinu, the Torah carries the authority to guide our lives and affect our behaviour. Without that root, as a poorly edited scroll writen by Ezra haSofer, it loses any authority and becomes as meaningful to us in the here and now as the Epic of Gilgamesh. Thus Prof. Kugel's own attempt to maintain his sense of Jewish belief and morality (he calles himself Orthodox, after all) is undermined by his research. Having removed the divinity of the Torah, how can he claim any form of morality exists in the Torah that is applicable to us? Because it sounds nice?
Perhaps the most damning for the Documentary crowd, however, is the existence of the Talmud and the various commentaries on the Chumash down to recent times. Only one who is wilfully blind can miss the fact that Chazal noted all the so-called contradictions in the Torah themselves and struggled mightily to explain them all. More modern commentaries on the Torah, specifically those of Rav SR Hirsch and the Netziv, summarized these efforts to show that these so-called "poor editing jobs" all serve purposes.
For the secular crowd this is considered an exercise in apologetics. But a look at the explanations of Chazal clearly reveals why the secular crowd needs to dismiss them so strongly. The irregularities in the Torah itself serve as hints at the Oral Law which was given to Moshe Rabeinu at Har Sinai along with the Written Law. Missing letters, varying versions of the same event, repeated statements, all these serve to hint towards the corresponding section of the Oral Law which the people were taught.
For the secular crowd, there is no Oral Law. It was all an invention of "the Rabbis" to increase their control over their flocks and make sense of an unreadable Torah. For the believing crowd, however, the so-called mistakes lead to proof of the Oral Law's validity and hints at a superior, Divine morality at work.
Thus it is that an educated Jew who knows his Talmud and these important commentaries need not be seduced by the empty promises of academic truth and intellectual honesty the Documentary Hypothesis crowd proposes. Their agenda is to eliminate objective morality from the world so they can enjoy their hedonistic lives wihtout restraint or guilt. Our agenda is to keep God's presence in this world through the knowledge and practice of His Torah. Ours will endure far longer than theirs.