Okay, these are right from the source, actual passages from the Koran:
The Immunity
[9.1] (This is a declaration of) immunity by Allah and His Apostle towards those of the idolaters with whom you made an agreement.
[9.30] And the Jews say: Uzair is the son of Allah; and the Christians say: The Messiah is the son of Allah; these are the words of their mouths; they imitate the saying of those who disbelieved before; may Allah destroy them; how they are turned away!
[9.63] Do they not know that whoever acts in opposition to Allah and His Apostle, he shall surely have the fire of hell to abide in it? That is the grievous abasement.
[9.64] The hypocrites fear lest a chapter should be sent down to them telling them plainly of what is in their hearts. Say: Go on mocking, surely Allah will bring forth what you fear.
[9.65] And if you should question them, they would certainly say: We were only idly discoursing and sporting. Say: Was it at Allah and His communications and His Apostle that you mocked?
[9.66] Do not make excuses; you have denied indeed after you had believed; if We pardon a party of you, We will chastise (another) party because they are guilty.
[9.73] Prophet, make war on the unbelievers and the hypocrites and deal rigorously with them. Hell shall be their home: an evil fate
Note that the name of the chapter is "The Immunity". Basically, if you are Muslim, if you choose to go and do anything in the name of Allah, you are justified and righteous.
Actually, Islam holds that Christians and Jews are both "believers" as they recognize the one and only god (allah, which means "god", it's not a name like "Jesus"). Islam, through its pillars, views Christians and Jews as "protected peoples" since they fulfill the most important criteria of all - the recognition and worship of the one and only god. Their non-recognition of the prophet Muhammad (secondary in importance) and their non-adherence to the same practices as Islam are what prevent them from equal status. Islam reveres the Torah/Old Testament, as well as Jesus' revisions to it. They revere Noah, Abraham, Moses, Jesus, etc. as prophets. Nothing in those passages states that Muslims should kill non-Muslims, it just says they'll burn in hell/be punished by Allah. Even when the prophet's told to do something, that doesn't extend to everyone any more than the entirety of Islam should prophesize because Muhammad did it. There's no shortage of that kind of tripe in the New Testament or Torah either. As God/Allah/Jehova-Elohim/Whateverfantasybeing says: "Vengeance is mine", not any indignant, deity-worshipping twit with the means and inclination.
As far as tolerance and civility go, Islam's got a much better track record than Christianity, even towards Christians - the Pact of Umar was far more than Christians were offering around the same time. It just so happens that the more intolerant, radical parts of Islam are empowered and active right now. The squeaky wheel gets the oil and all that.
Not saying that Christianity doesn't have it's own harsh passages:
Gen 4:15 And the LORD said unto him, Therefore whosoever slayeth Cain, vengeance shall be taken on him sevenfold. And the LORD set a mark upon Cain, lest any finding him should kill him.
Exd 4:22-24 And thou shalt say unto Pharaoh, Thus saith the LORD, Israel [is] my son, [even] my firstborn: And I say unto thee, Let my son go, that he may serve me: and if thou refuse to let him go, behold, I will slay thy son, [even] thy firstborn. And it came to pass by the way in the inn, that the LORD met him, and sought to kill him.
One does not need to be an accomplished scholar to go through a religious text to find scriptures that can justify violence. If someone put their mind to it, you might find something in Buddhism to justify killing for it.
I agree, though I think you might be hard pressed on the Buddhist thing.
I may be getting out of my lanes, but I read an article (of course can't find it now) but it spoke of religious maturity and how these things go in cycles. The way the Islamic extremists are conducting themselves isn't so different than the zealotry of the Crusades, and the Inquisition. Those took place about a 1000 years ago or so. So how old is Islam? The Prophet Muhammad died in 632, and the religion didn't get big enough to get noticed by the Christian church until 1096 when the first crusade was launched to take back the Holy land from the Turks (although arguably just an excuse for a Catholic land grab). So is it possible that this extremism is a natural progression of a large organized religion, compounded by the fact that by it's very design Islam is a very intolerant and harsh religion? I'm not suggesting that we ignore them and let them bomb and murder at will. But maybe they will realize, within their own ranks, that they have gotten a bit off course and bring things back to something a little more reasonable.
I've wondered the same about the development of religions. I'm not sure they're really all that different from civilizations/societies - they go into and out of bad spots, often depending on the economic, political, environmental, and other changes/effects. That's not to say they're separate from civilizations/societies or that there isn't some reciprocal effect there. I don't think violence, ignorance, etc. is intrinsic to Islam any more than it is to Christianity or Judaism. Each have their militants, it's just a matter of how much power they hold and how much publicity they get. I think Kirkhill explained it best.
And as an aside (since we can't seem to shake the cartoon debate) how can anyone get upset about making a cartoon with Muhammed in it? If it is Koranic law to not make any depictions of him, how does anyone know what he looks like? If you don't know what he looks like, how can you get pee'd off when someone draws him? Must be a dumb Christian thing 
Islam isn't the only religion which is touchy about visual representations - if you read the Torah, you'll find plenty of condemnations of idolatry and I don't think you'll find many Jews drawing or using images of Abraham, Moses, Noah, etc. in their religious practices or even at all, for that matter. I could be wrong, though. I don't think this cartoon crap would be nearly as much of an issue if the climate of relations between the Islamic world (especially the Middle East) and the historically Christian world (IE the West) weren't as messed up as they currently are.
There are all sorts of idiots right now of every denomination, ideology, etc. that scream for the death of someone for little reason other than they're angry. Just look at Ann Coulter and the other right-wing morons espousing crap like forced religious conversion for Muslims, making the Middle East a "parking lot", calling Muslims (or anyone with slightly darker-than-Nordic skin) "towel heads" "sand-n******", making stupid, ignorant, misinformed statements about the nature of Islam (and by extension, Muslims), and my personal pet peeve - referring to Muslims as "hadjis", which isn't necessarily insulting (though it often seems intended to be), it's just stupid.