They all study and memorize the same book and that book is explicit about how a Moslem is to treat nonMoslems. They are to lie and to kill and to force conversions until all the world is Islamic. Christians are exhorted to go and convert all people by bring them the good news. The implication is that it all depends on the persuasiveness of the Christians. Moslems are exhorted to convert and to conquer or kill until all are Moslem. The implication is that any means is acceptable to that end. All must be made Moslem or eliminated, not all must be given the information to make up their minds.
All Christians use the same book, yet how they interpret it and the way they practice can be quite different.