Nah, you're not very knowledgable yourself. I'm not an expert either but at least read up a bit on history rather than referring to wacky websites. You're mentioning one of their historical justifications, but one of minor importance. (It's also among the most silly ones, because the Kalifats they admire so much and wish to rebuild were at their height at a time when the Muslim world was the most tolerant, when people of all faith were living together without problems while Christians were slaughtering each other in Central Europe.)
If you want to understand the motivation of these terrorist movements (which are pretty evil, no doubt about that), you need to look at the colonial history of the Middle East and how the French, Brits and the US messed up the region. And if you think that's the past and they have learned from their mistakes, think again, because they have just repeated them in Iraq and, very recently, in Egypt. When you install dictators and puppet military juntas in foreign countries and the only notable opposition left is radical islamic, then you ought not be surprised if radical islam arises in the long run.