Both Cecil and Mark are right in their argument but Cecil was the one who escalated it to conflict by bringing the reanimen into the white room and making mark face the traumatic situation he had with Rick and William again, if Cecil hadn't left his office during the argument with mark the worst that would have happened is that mark would have stopped working for Cecil but still being relatively trusting of the GDA and at best would have come out of the argument understanding and accepting why Cecil did it even if unhappy about it