Buenchico;//On the other hand, the (nominal) justification for the Crusades was precisely the slaughter of those of whose religious beliefs differed from those of their attackers.//
You claim to have read both the Bible and the Quran (entirely?), perhaps you should now bone up a bit on your history. The aim of the crusades of the 9th and 10th centuries was to RE-conquer the holy lands and parts of Southern Europe from the Muslims who had been the ones doing all the slaughtering.
Charles Moore, Spectator's notes; 01/08/2015, on a recent visit to Portugal;
"... In Britain we have had until recently, so little direct experience of this conflict with Christendom that it is not much part of our folk memory, but in the Iberian peninsula the idea of what Mr Cameron calls am 'existential threat' is old and deep. We saw two depictions in churches in Oporto of the beheading of Franciscan friars by turbaned Moors. It was a shock to sense that what would until recently have seemed thankfully out of date, now felt contemporary.
In Bento station in the same city, handsome azulejos murals, a century old depict the conquest of Ceuta in 1415 by King John of Portugal and his son Prince Henry the Navigator, before whom the Moors throw down their arms and beg for mercy. One wonders how long before such a scene is removed for being Islamophobic."