A major problem our world has today is the inability of most people to distinguish between followers of a religion and the founders of it. By their very nature, the founders of a religion get to define it. A follower, by contrast, must believe what the founders teach/taught. Otherwise, depending on the degree of deviation, they cease to be followers, but instead become founders of their own religion, or the followers thereof.
Using this logic, we can establish a major flaw in all attempts to claim that Christianity is a violent religion. See, Jesus is the founder of the Christian faith. Even if you aren't a Christian, all that does is shift the founding of Christianity to the Apostles, who claimed to be acting under His inspiration, and on His authority. They believed themselves to be mere stewards of the mysteries of God (1 Corinthians 4:1), acting under the inspiration of God (2 Timothy 3:16-17), and with evidence they saw with their own eyes (2 Peter 1:16). Thus, even if you don't believe Jesus is the founder of Christianity, that only shifts the founding of the faith to His chosen students. Everyone except the New Testament authors fits into one of the following categories:
- Follower
- Heretic
- Apostate
- Unbeliever
Follower
As the name suggests, followers of a religion follow that religion. If you're a follower of Christianity, it means you at least try to learn and apply the teachings of Christianity. Thankfully, these are all laid out in a book called "the Bible", which, with huge leaps in technology, is now available virtually anywhere on Earth, in many languages, free of charge, at the touch of a button. Of course, even with this, it is possible to deviate from Christian doctrine while remaining Christian.
Heretic
A heretic is someone who claims to be a follower of a religion, but has deviated from the faith in some major way. While the sources of a religion clearly teach one thing, a heretic believes something entirely different. In Christianity, for example, the doctrine of the Trinity is clearly taught in Scripture, yet many who claim to be Christians reject this doctrine. This deviation is so severe that those who do it cannot legitimately be considered Christians, both due to the importance of the doctrine, and due to its clarity in scripture.
Strictly speaking, a heretic may also be a true follower of Christianity, because there is a distinction between an essential and non-essential doctrine. Rejecting a non-essential doctrine may be an indication that someone isn't Christian, but does not, in and of itself, make them a false Christian.
Apostate
Apostates are those who used to claim to be followers of a given religion, but no longer do. Due to the doctrine of the Perseverance of the Saints, there are many side debates that could take place regarding whether ex-Christians even exist. I know in my own experience, most ex-Christians, even those who claim to have been in the faith for decades, often display very little knowledge of the Christian faith, certainly less than they would be expected to have if they were truly invested in it. That's not to say they are/were insincere, of course. If you hear someone claim to be an ex-Christian, there's a 99% chance they believe it. It's an error, not a lie.
Unbeliever
Unbelievers are those who never claim to be of the faith in the first place, or if they do, it's insincere, usually for some form of gain, or, if under persecution, defence against loss. Christianity obviously has its fair share of unbelievers.
All 4 groups are poor benchmarks
Suffice to say, unbelievers and apostates are a poor benchmark for whether or not Christianity is a peaceful religion. Not that most people do this (although some people have attempted to attribute the actions of Anders Brievik, a self-proclaimed Odinist, to Christianity).
Just as unbelievers are poor benchmarks for Christian morality, so also are heretics. After all, in a sense, heretics are still unbelievers. Christian: "This is what the Bible says." Heretic: "I don't believe that, I believe this instead." Ok, you're an unbeliever. You literally do not believe the Christian belief, therefore how are you even able to call yourself a Christian with a straight face?
But even believers, due to the unfortunate state of humanity, are a bad benchmark for Christianity. Human beings, after all, are flawed. New converts might not have read the Bible. Even more mature believers might not have read the whole thing. And while reading it is a start, it's no good if you're not retaining it. Retaining it is also temporary, revision is necessary. Furthermore, retaining information is useless if you don't understand it. And of course, at the end of the day, anyone who says he is sinless is a liar, even to the degree of lying to himself (1 John 1:8). There are many reasons even a true follower of Christ may deviate from the faith in some way, shape, or form, and for that reason, they should no more be used as an indicator for what is Christian than a thief should be used as an indicator for what is legal.
Words have meaning
Of course, there is one response every unbeliever loves to make whenever a discussion isn't going their way. "How do we know your interpretation is correct?" Answer: The same way you know I believe Christianity is a peaceful religion! You are reading this article the same way everyone should be reading the Bible, i.e. with intent to discover the interpretation the authors intended to convey. Due to the nature of language, this is actually very easy to do.
I can tell you this much, there is no sensible way to interpret "Love your enemies, bless them that curse you, do good to them that hate you, and pray for them which despitefully use you, and persecute you;" (Matthew 5:44) as "hate those who aren't Christians, persecute those who are different from you". And tell me, what do you do with Romans 12:18? "If it be possible, as much as lieth in you, live peaceably with all men." Well, that's obviously telling you "if anyone leaves the Christian faith, kill him". Clearly, we as Christians are supposed to fight the unbeliever wherever we find them. No! When the Bible says live in peace with all men, it means live at peace with all men!
And the part where it says "If possible, as much as it depends on you"? Well, guess what, Christians are allowed to defend ourselves, and are in fact commanded to rebuke the oppressor, speak out for the voiceless, and defend the defenceless. It's not always possible to live peacefully with all men because some men are not committed to living peacefully with you. The Taliban, for example. How do you live peacefully with men who, now armed with a shed load of military weapons left behind due to a disastrous decision by an incompetent president who shall remain nameless, abuse, and even kill, anyone who doesn't submit to their particular brand of Islam? If you believe Christianity is a violent religion because it is not perfectly Pacifistic, it's safe to say that you are actually the violent one, because Pacifism is the perfect ideology to ensure violent men continue to grow in their capacity and desire to be violent, whereas the defensive use of violence, and even in some cases the offensive use of violence, is often necessary to restrain them.
Conclusion
So, is Christianity a religion of peace? Absolutely, and indisputably, yes. Anyone who says otherwise may have their reasons. For example, if you haven't read the Bible, but have read The God Delusion, you might well be convinced that God is "...arguably the most unpleasant character in all fiction: jealous and proud of it; a petty, unjust, unforgiving control-freak; a vindictive, bloodthirsty ethnic cleanser; a misogynistic, homophobic, racist, infanticidal, genocidal, filicidal, pestilential, megalomaniacal, sadomasochistic, capriciously malevolent bully." But if you have read the Bible, you'll easily see that such a loquacious tirade is misleading at best. With Jesus being the exact image of God (Hebrews 1:3), and going by the Christian Scriptures, no literate person has an excuse for believing Christianity is a violent religion.