The problem with terrorist attacks conducted by Islamist radicals compared to their non Islamist counterparts is the scope of those attacks as they transcend national borders and are not confined to a certain region or location, it's more of a global worldwide theater of operations for them unlike the usual terrorist organizations in Europe or the US.

Also, I have reservations including nationalist movements and lone-wolf ops in your rebuttal as the underlying nature of the struggle is completely different than that of the Islamic terrorism. You could reason with a radical nationalist and persuade them to explore other options than an armed struggle to reach political goals but good luck trying that with a faith-driven, theology-loving radical who thinks he's on some divine (read: apocalyptic) mission to cleanse the masses of their imaginary sins.