FYI The X in xtian is not actually a letter “x” its actually comes from the greek letter “Kai” which was short for the meaning our lord and savior
So there is no difference between writing xtian and christian.
Now its a “Aveirah” to read secular books, I guess all those Rabbanim who are the heads of Bais Yakkovs, Many Boys Yeshivas, YU, and Touro are major reshiam. Not only have they read secular literature they have encouraged good Yingerlach to sin greatly