Why did the Zaydis and the Khawarij agree on denying intercession?

Intercession (Shafa'ah) is affirmed by the Qur'an and Sunnah, as in His (Allah's) saying, "Who is it that can intercede with Him except by His permission?" (Qur'an 2:255), and the Prophet's (peace be upon him) saying, "My intercession is for those among my Ummah who committed major sins." It is affirmed for the prophets, angels, martyrs, and the righteous. The Khawarij and Zaidiyyah denied it, citing verses and Ahadith of warning (wa'id), which are intended for disbelievers and those who died in a state of disbelief. The methodology of Ahlus-Sunnah wal-Jama'ah is to reconcile the texts of intercession with the texts of warning. The warning is specific to non-monotheists, or its judgment is left to the will of Allah the Almighty.