You really need to read a bit more history before you opine.
I looked into it a little more and it seems to be not very open and shut on whether the Christians were responsible or not. I got the story from Carl Sagan who is not exactly an unbiased source. As to the Caliphate --
http://www.bede.org.uk/library.htm
>The errors in the sources are obvious and the story itself is almost wholly incredible. In the first place, Gregory Bar Hebræus represents the Christian in his story as being one John of Byzantium and that John was certainly dead by the time of the Moslem invasion of Egypt. Also, the prospect of the library taking six months to burn is simply fantastic and just the sort of exaggeration one might expect to find in Arab legends such as the Arabian Nights. However Alfred Butler's famous observation that the books of the library were made of vellum which does not burn is not true. The very late dates of the source material are also suspect as there is no hint of this atrocity in any early literature - even in the Coptic Christian chronicle of John of Nikiou (died after 640AD) who detailed the Arab invasion. Finally, the story comes from the hand of a Christian intellectual who would have been more than happy to show the religion of his rulers in a bad light. Agreeing with Gibbon this time, we can dismiss it as a legend.