They were anonymous to the extent that the authors did not write their names in them. That does not mean that the books turned up in congregations without people knowing something about who wrote them. Traditions have to start somewhere.
They were anonymous meaning that no one had any idea who wrote them, nor at that time was there any claim as to who wrote them.
Sometimes traditions have a root in something historical, but most of the time they do not. Traditions can be entirely fabricated, or based on misunderstandings.
Sally's husband asked her why she always cut off both ends of the roast before putting into the oven. Sally said, I don't know. It's the way my mom taught me to do it.
So Sally goes to her mom and asks why. The mother replies, I don't know. It's just how grandma taught me to do it.
So Sally's mom goes and asks grandma. Grandma says, "Well, it's because our pan was too small."
Tradition is just part of what we call "history".
No it is not. Sometimes it can be related to history, but don't confuse it with history. Tradition is something that is passed down because it is meaningful, not because it is factual. History on the other hand is not based on whether someone likes it. It is based on evidence such as reliable sources or archeological finds.
Maybe it is considered less reliable, but written history can begin with oral tradition, which gets written down.
Absolutely not. History is never based on tradition. In the first century, the science of history was in its infancy. Even well recognized historians like Josephus weren't that careful of their sources. But today, history does consider tradition or stories orally passed down to be legitimate sources.
The traditions about who wrote which gospels do fit the internal evidence we have from the gospels and other parts of the New Testament however.
What "internal evidence" do you have that John wrote the gospel of John, or that Matthew wrote the gospel of Matthew? Absolutely none.
From what I can see, the only evidence there is, is that the traditional authors are the right ones.
There is no evidence of ANY particular author. In fact, if you consider the textual analysis, the gospels all had more than one author whose works were spliced together.
Those that want us to believe otherwise seem to be basing their argument on the idea that the supernatural is not true
No, it's based on the lack of affirmative evidence, and actual evidence to the contrary.
and so Jesus could not have prophesied about the Temple destruction and so the gospels were written after 70AD and so they are lies from the start and probably by people who did not know Jesus or know his followers.
Because although many views may be possible, not every view is plausible. If there is a perfectly natural explanation for something, it makes no sense to ascribe a supernatural reason. Did I use this example with you earlier?
This morning when I woke up, there were sprinkles of cat litter on the floor near the litter box.
A. My cat used the box during the night, and tracked a bit of litter out.
B. Angels visited my home and levitated the litter from the box to the floor.
Do you see from that how unreasonable it is to claim a supernatural reason when there is a perfectly natural explanation?
It diminishes it as much as being a conservative scholar of the Bible diminishes a person's scholarship.
Theologians are only one kind of scholar, and their expertise is in the interpretation of the texts. The scholars I'm speaking of are the experts in textual analysis, which is science, not religion. Since none of the gospels say, "I, Matthew (or whatever) am writing this to you that ye may...", the authorship of the books is not the purview of theologians. It is the purview of textual critics.