Having become stronger than the Warlocks of Silvermoon, there was a Fel magic practitioner named Assyd. Assyd is an Archaeologist, and she discovered a tome from not even that long ago. In the book she found that female Warlocks were actually called Witches. So she created a coven. She called it, "The Order of the Fel Witch".
When she found a pupil, she decided that She, Assyd, was the Fel Witch.
Frustrated and outright angry with the efforts of the Warlock Gul'Dan, Assyd thought it prudent to ignore his desires and vision of what the relationships of the living and the demons should be. Knowing that the destruction of the living would void any agreements the Fel order had with their demons, and allow the demons to overpower them.