The exact quote from the show in episode 3: "In these last ten years the Turks have taken Belgrade. They have lit their campfires in the great library at Buda. It is only two years since they were at Vienna. Why would you want to make another breach in the walls of Christendom?"
Just like to leave a comment here pinging u/Fornad and an excellent answer to a question concerning the fall of Constantinople to the Ottomans and its reception by Christian elites.
While the two settings are decades apart perhaps some of the attitudes could be shared by these elites? Also given that it’s Thomas More we’re talking about maybe he had written something on the matter of the ‘Ottoman threat’?
EDIT: forgot to actually leave the link here.