Islam, in general, isn't violent. They're just like any other religious culture.

Most of the people in countries like Iraq and Pakistan would be Muslim. Now when people from distant nations order their population to go and invade a country unprovoked, there will be more than violence. Thousands, if not millions, of innocent people being killed, just to get a handful of "bad guys"?
Forget about religion; If people came to your country and started killing your friends, family, and communities all around you, wouldn't you want revenge, or at the least attempt to protect your people?

It's not about the religion, really. Most cultures would react the same.