Some thoughts...

This is not written as a formal paper or argument, so do not judge it as such.

Christianity and its many forms call for proselytizing, as does Islam (and many others I'm sure). Throughout history, both religions have held a viewpoint of "Convert or die!" Sadly, that viewpoint is still in existence today. The holy books of both religions give examples of such ideology and/or call for the death of unbelievers. Thankfully it is only the more extreme, hardcore believers that would still put that ideology into practice today, but such an awful concept is displayed and put into the minds of all who read/hear. My knowledge of Islam is limited, so I shall now speak about what I know - Christianity.

The Old Testament is full of stories in which people, such as the Canaanites, are slaughtered (usually without being given the chance to convert) simply because they aren't Jews, they don't believe in the right god, and they own the land the Jews want. As a child, I found the OT both fascinating and disgusting. The bizarre stories it contained were largely skipped over by my teachers and pastors (probably because of the confusing and even horrendous nature of said stories) at both church and school (I attended a Christian school), but I still read through my Bible and found them. When I attended a Christian college, and we worked through the whole Bible in two survey classes, the bizarre stories came to light again, and were passed over by the teacher either entirely or after he'd only said a few words. We discussed the children of Israel and their long battle to claim Canaan, but no-one ever said a word about how awful it was that they were being ordered to massacre people. During the time of the OT, if you weren't a Jew, tough luck - you're either going to be serving the Jews, distant enemies, or massacred for your land (unless you were lucky enough to be a virgin, and God said they could take you alive, which didn't always happen).  Once you hit the New Testament, this ideology largely disappears, because now Jesus is telling the Jews to love their neighbors, enemies, and everyone else. The Jews of the OT were an exclusive bunch and did very little proselytizing. In the NT, Jesus seeks for converts, but focuses on the Jews. It isn't until after Christ's death that the conversion of gentiles is sought after. From that point on, history is full of Christian attempts to proselytize the rest of the world, be it with love or force. Heretics are burned at the stake (even by such illustrious leaders as John Calvin), those suspected of witchcraft are tortured and killed, and on the list of things done in the names of Christianity and God goes.

A Brief Book Review (with quotes)

The following paragraphs are quoted from Christopher Hitchens' book god is not Great: How Religion Poisons Everything (capitalization as printed by the author). I discovered this book at my local library, and found it to be a very interesting read. The author is a staunch atheist, so I disagree with him there, but his overall look at religion was both intelligently written and fascinating to read. I would highly recommend reading it (if you are an open-minded person and not one to have your feelings easily hurt, as he is not "nice" at times), particularly the chapters on the Old and New Testaments. I typed out these particular sections (all italics are the author's), but would have liked to type out the whole chapters he wrote on the Old and New Testaments - they were that good.

"Ask yourself the question: how moral is the following? I am told of a human sacrifice that took place two thousand years ago, without my wishing it and in circumstances so ghastly that, had I been present and in possession of any influence, I would have been duty-bound to try and stop it. In consequence of this murder, my own manifold sins are forgive me, and I may hope to enjoy everlasting life.
Let us just for now overlook all the contradictions between the tellers of the original story and assume that it is basically true. What are the further implications? They are not as reassuring as they look at first sight. For a start, and in order to gain the benefit of this wondrous offer, I have to accept that I am responsible for the flogging and mocking and crucifixion, in which I had no say and no part, and agree that every time I decline this responsibility, or that I sin in word or deed, I am intensifying the agony of it. Furthermore, I am required to believe that the agony was necessary in order to compensate for an earlier crime in which I also had no part, the sin of Adam. It is useless to object that Adam seems to have been created with insatiable discontent and curiosity and then forbidden to slake it: all this was settled long before even Jesus himself was born. Thus my own guilt in the matter is deemed "original" and inescapable. However, I am still granted free will with which to reject the offer of vicarious redemption. Should I exercise this choice, however, I face an eternity of torture much more awful than anything endured at Calvary, or anything threatened to those who first heard the Ten Commandments."
~ pg. 209-10