Legitimate textual source questions

I came across a comment that suggested that source criticism is acceptable for Christians when dealing with the gospels but not the Pentateuch. Presumably that means discussing how Luke and Matthew are dependent on Mark is permitted but finding the Elohist and Priestly divisions of Exodus is not? I assumed that this remark was reflecting a cynicism on the limitations, and even hypocrisy, of biblical critique within Christendom (or perhaps evangelicalism).

I can see why such an idea may come from but I believe it is unjustified. Such comments imply that non-Christian criticism is less biased. This is not the case however.

The source question is somewhat apparent in the gospels. They are called the synoptic gospels. It is evident to readers that Matthew, Mark, and Luke are similar in many ways and, while distinct, together they are moderately different from John. Thus a source question arises naturally from the text. As it does with Jude and 2 Peter, or Chronicles and Kings. This type of source question is considered legitimate in both the Old and New Testaments.

The Pentateuch is not comparable to this situation. While there is overlap amongst the books, especially with Deuteronomy; the source debate is not about parallel texts in the Torah, it is about deconstructing the text.

It is not entirely true that source criticism is not "allowed" here. Some conservative scholars think that Moses compiled Genesis largely from extant texts that antedated him. They base this conclusion on the toledoth theory.

So one reason is that source differs between the 2 texts. One looks to the source of similarities between parallel texts, the other looks to the source of a text assumed to be disparate. Another significant reason is that many Christians reject the suppositions of persons who originated the theory. People that were antagonistic to both God and Scripture. This is especially warranted given that several of their assumptions were incorrect: such as the belief writing had not been invented by the time of Moses. Frankly, if their foundations are absent then their edifice is broken and will remain so despite attempts to repair it.