I'd like to pick a few bones here and there. As Richard Carrier had pointed out, there does not have to be a great conspiracy to destroy ancient pagan writings -- only lack of interest. Thus, as RC notes, we have lots of surviving copies of Jerome's letters, and not various things that would have been much more valuable.

But Kelly is right about pressure. Sir Isaac Newton, hailed as a saintly religious scientist, rejected the Trinity -- and he kept his Trinity rejection secret in order to avoid endangering his career. Sir Francis Bacon seemed like "the lady doth protest too much" when he claimed that a "little" thought leads to atheism. The philosopher Benedict Spinoza was excommunicated by the Jewish community and denounced as an atheist for what he called "God". Etc.

And to see what it was like to duplicate a book in pre-Gutenberg days, try doing so yourself. Take one of your favorite books and make a handwritten copy of it. And do so without a pencil or a ballpoint pen -- instead, the old-fashioned kind of pen that you must dip into an inkwell. And do so in a clearly-readable handwriting style and without making a lot of typos or corrections or inkblots.

Several books survived the Middle Ages by being recycled; the original content was scraped off and something else written on it, making a palimpsest. Thus, one of Archimedes's books survived because someone used its pages to write a prayer book on it. Yes, that was the favorite sort of literature of medieval scribes -- Bibles, writings of Church Fathers, hymn books, prayer books, biographies of saints, ...