i agree with hanibal, you may hate khawarijites but every historian acknowledges that Khawarij were extremely comitted to their ideology, they put there life where there tongue was. Even a few hundred Khawarij could kill few thousand of army.
This is why comparison holds with Khawarij. Just like them, Taliban are extremely committed to their ideology, and just like them they consider anyone disagreeing with them as kafir and worthy of execution.
Khawarij were extremely pious. Many of them had nishan e sajda on their forehead.
So anyone considering himself pious does not necessarily make him one. Prophet's hadeeths also show this. Taliban and khawarij are examples.