Yes, and I am more than aware of that. However, you need to bear into account the person who chose to present those texts together and acknowledge their judgement. The bible is portrayed as a book and therefore it is hard to say it would be fair to judge one element of it without acknowledgement of everything else. Which does not necessarily mean acceptance.
By your criteria how could we judge anything? Would you throw away Nietzsche's works because he was raving mad when he wrote some of them or would you judge his whole message with knowledge of how his life changed his viewpoint.
Who is to say there is accuracy consistent throughout a single source? All we can do is to try and get as close as we can to the time of the person and the proximity of the person. But to completely discount something that is intrinsically connected is equally as daft as accepting one component of the bible as fact and then decreeing it all as fact.
Your argument would mean we would never use an encyclopedia or wikipedia and then these forums would be royally screwed. I mean if we had to evaluate every source without checking it's authenticity. A global check allows us to assume things with a degree of confidence of not.
There is an element of truth in what you are saying, however it is common with multiple texts to treat each individually, it is also common with ancient texts to treat each separate contextual subject separately as well, Josephus'
Antiquities of the Jews is a good example of where each element within the text is authenticated and judgements made on it's reliability therein.
The problem is that you make the very common mistake in assuming that the Bible is considered as a single Book, it is not, even the title "Bible" infers that it is a collection rather than a single tome. Much depends on what you are trying to accomplish, if you are making a historical assessment of the Bible then each part would be taken in isolation, even within some of the texts themselves certain aspects may be treated in isolation, This is not to say that they are not compared to and assessed against the other elements of the Bible or from other external sources. Quite the contrary, it simply means that for the purposes of assigning authenticity and assigning reliability each is treated separately to one degree or another.
However if you were making a theological assessment of the Bible then you would treat each Testament individually as well as each Book within each testament...you would also see how they relate to each other and other extant texts theologically, you would not generally assess them in isolation, although as we see often in GD people do that all the time, which is kind of ironic considering some peoples opinion on how the bible should be judged.
That is not to say that a Historian or a Linguist doesn't consider the whole and how each passage relates to each other, to extant sources, external texts such as those related to Heresiology etc... Linguists especially look for repetition and similarity especially when trying to ascertain context from texts attributed to the same author or groups of authors, time periods, cultural periods and so on.....
The problem with the Bible is that it was never meant to be a history book as such, it was simply a consensus of Early Christian and Hebrew writings that was thought portrayed the message common to Christianity at the time....it was never designed to be historically accurate or a treatise such as Tacitus'
Annals or Josephus'
Antiquities of the Jews .
There is much to be learned about ancient history in the Bible, and there is a lot that will not match up to archaeological or other historical and source text evidence, although any ancient historian or archaeologist will tell you that both of their fields are subjective to a great degree and the same with regard the Bible.
Pretty much anything prior to the end of the Ancient Classical Period with Justinian I is subject to significant interpretation and often it is only by consensus(you should see just how much argument there is over the significance of a single letter or word amongst my peers, let alone a whole passage or document) that events and people are deemed to have reliably existed at all.
