Why are there forgeries in the bible?

I would like to focus on the New Testament for this thread, since I haven't really studied much of the Old Testament.

Of the 27 separate books in the NT, only eight books, just eight, have been established as authentic, meaning they can actually be traced back to the original author.

The authenticated books include seven letters written by the Apostle Paul (aka Saul of Tarsus):

-Romans
-1 and 2 Corinthians
-Galatians
-Philippians
-1 Thessalonians
-Philemon

The other authenticated book is the Revelation of John, although no one knows exactly who this John really was.

The rest of the 19 books of the NT are forgeries, yes FORGERIES. They include gospels that were written anonymously but later had the names of disciples added to the works, to give the appearance that they were actually written by a disciple when they actually were not.

Other works from the NT include letters that were outright forgeries, written with intentional deception, to trick readers into thinking they were reading a work by someone important, such as the apostle Paul or Peter, when they actually were not.
Some of the outright forgeries include:

1 and 2 Peter
2 Thessalonians
Colossians
Ephesians
1 and 2 Timothy
Titus

It is accepted by many critical scholars that the books listed above and others were not written by the authors claimed to have written them. They are forgeries in one way or another.
Forgeries and plagiarism were actually quite common in the ancient world and early Christianity is littered with examples of this.

Now let me ask this question.
Knowing full well that the New Testament does contain forgeries, how can one justify their faith and belief in light of this damaging evidence? And keep in mind, I'm just focusing on the biblical forgeries for this thread. Other issues, like contradictions and discrepancies in the bible, I'm not even taking into account.

Sources:
If you wish to have more in-depth information on biblical forgery, check out Misquoting Jesus by New Testament historian Bart D. Ehrman. His other book, Jesus Interrupted, is fantastic as well.