Just think one moment about the fact why someone or a group would want to kill the third khalifah of the muslims Uthman ibn Affan (radiallahu anhu), then you would understand the mentality of the deviant takfiri and extremist khawarij, may Allah save the ummah from them, ameen.
Uthman ibn Affan (radiallahu anhu) was the rightful Khalifah of the muslims, just like Ali (radiallahu anhu), he had a Khilafah and ruled with the shari'ah, still the Khawarij of that time did takfir on him and Ali (ra) and killed them, subhan'Allah!
So this shows that it is impossible to talk and reason with those people! If they were not happyh with Uthman and Ali (radhiyallahu 'anhum ajma'ien), do you think they will accept Amirul Mumineen Mullah Omar and Al-Zawahiri, may Allah protect them?
One of their forefathers even said to the prophet (peace be upon him) when he was busy distributing some goods: 'be just!'. The prophet (pbuh) said: 'who would be just if I am not just?'.
This shows their extremism and evil hearts and sick mentality! He thought he was even better than the prophet! What an arrogance and haughtiness!
The islamic definition of kibr (arrogance) is looking down upon others and not accepting the truth when they say it!
The prophet (pbuh) said that the ones who have an amount equal to an atom of kibr in their hearts will not even smell paradise, let alone enter it!