While there is something to that, since such a bizarre associations does indeed attract people who want to commit violence and feel justified while so doing, it is not a very good explanation.
For one thing, it applies perhaps better to Islam. The Crusades were a very long and confused affair, but I don't see that it would motivate Muslims much too differently than it would Christians. Of course, neither do you claim otherwise. I just wanted to mention this.
Still, I think the true reason is more wide in scope. In its current form, Christianity is a religion that draws upon fairly universal needs for authority and rulings, while at the same time not really demanding much knowledge or dedication to include one among its ranks (Christianity makes a point of encouraging people of uncertain allegiance to try and stay with it for the time being).
I actually think this is something of a subversion of religion's role in society, albeit a numerically very succesful subversion.