As I understand the problem, AU Draenor is drying up or dying in some manner and both sides blame one-another for it, with no real conclusive proof as to who is responsible or why. Yrel and the Lightbound blame the Mag'har for doing *something* to be causing the issues, and Grommash blames Yrel and the Light for it. We're never actually shown who or what is responsible for what seems to be happening to their world.
That having been said, the fanaticism of the Draenei and their desire to forcibly "convert" unwilling Mag'har to the Light is detestable on the face of it - all conversions by the sword generally are. Just like Xe'ra's decision to try to detain Illidan and force the Light upon him, altering his destiny and taking from him his free will was detestable. The Light shouldn't be forced on anyone, and any agent of the Light who would be so zealous as to try and do so is an individual worthy of stopping.