a) there are Christians physically persecuting/killing/attacking Muslims *somewhere* in the world (of course, this leaves doubt as to whether they are real Christians at all, let alone read their Bibles). I'm pretty sure that was the case in Kosovo, way back when.
b) honest, faithful, Qu'ran-believing Muslims would be all too quick to disown violent extremists, just as Christians would be quick to disown, say, the Ku Klux Klan; and could probably show you a verse in the Qu'ran that definitively condemns aggressive (as in non-defensive), violent action for any reason.