Lore wrote:
Not to mention the fact that even if it were the oldest that doesn't mean it's right. And they'll agree with that conclusion when they realize that some other religious text is older.
I think they've even shot themselves in the foot with the idea that oldest = right, so they can't even use the possible escape you suggest above. In the same paragraph that begins by saying the oldest portion of the Bible predates all other religious writings, it lists some various other religious writings and then says:
If some of these works are divinely inspired as some assert, then what they offer in terms of religious guidance should not contradict the teachings of the Bible, which is the original inspired source.
In the next chapter, it says:
It is not that all religions actually grew out of one religion, but the ideas and concepts should be traceable to some common origin or pool of religious ideas. - chapter 2, paragraph 27.
To sum up, it says:
In other words, going back to the analogy used earlier, the account in Genesis constitutes the original, crystal-clear pool from which stemmed the basic ideas about the beginning of man and worship found in the various religions of the world. - chapter 2, paragraph 40.
They seem to be saying that since the oldest Bible books are supposedly the oldest religious writings, all other religions drew their ideas from those Bible books, and that the validity of those other religious ideas must be judged according the Bible because it is the oldest.