In a sense this is restating the obvious, but sometimes the obvious is worth restating. Like all big religions, Islam not only has multiple well-defined subdenominations, but also varies greatly from time to time, place to place, and ultimately person to person. All of us know this about the religions we're most familiar with, such as Christianity and Judaism.
Is Christianity "a religion of peace"? Well, that depends on which Christians you're talking about, where they live, when they live, and what their personal temperaments are. Theological inquiries and quotations from the sacred texts will tell you very little about it. (The text and broad tradition of the religion likely influence practitioners' behavior in some degrees, but the result is very far from determinate, as the variety of Christian thought and, more importantly, Christian action, tells us.) There is no Christianity, only Christianities practiced by particular Christians and groups of Christians. Likewise for other religions. This doesn't make their warlike subgroups any less warlike, but it should make us skeptical of generalities about billion-member (or even million-member or likely multi-thousand-member) religions. Max Boot, who knows a lot about international matters, points this out in much more detail. Here are the first few paragraphs:
Given the monstrous crimes perpetrated in the name of Allah, it is easy to despair about the future of the Muslim world. Nonstop news about bombings, beheadings and general bedlam will no doubt lead more and more Westerners to conclude that we are at war with an entire civilization.
In reality, Islam has no fixed identity. Like other religions, it is based on vague generalities whose application varies widely across time and place. A thousand years ago, the Muslim world was a center of learning while Europe was mired in the Dark Ages. Today, the positions are nearly reversed. But there are many different rooms in Dar al-Islam (literally, "house of submission"), and no two are alike.
He goes on to give examples from Malaysia and Qatar; I can't speak with confidence about those, except to say that I'm confident he knows much more about those matters than I do. But his broad point is entirely right.