The Draneii (name meaning, the exiled ones) came on a spaceship, fueled by the power of the deity incarnate, a Naruu. There is no question for the Draneii that the Naruu exsists (they can go and talk to and touch them) and they are in fact so devout to the light that they all got something small as an ability called ‘Gift of the Naruu’ their fastness to keeping against the oppression of the fel they got ‘heroic presence’. They kept faith in the light and refused the gift of Sargeras. This is core concepts of the ‘race’ as a whole. They don’t only believe and have faith in the light - they were litterally guided and saved by it. They are as devout as any mortal can become - for they did in truth actually see the light.
The Lightforged are a subfaction of the Draneii. These are the religious fantatic templar warriors of their faith. They are infused with the Light. They are directly linked to the will of the Naruu.
Now, you can argue there are Eredar that lack faith or believe in other gods. These are not Draneii though. Draneii is a very spesific group within the race of the Eredar. The player character is a Draneii. Now, if they rename it to Eredar and removes the passives, I don’t mind much - but do understand, this is what people mean when they say “This makes no sense, why would they accept what they litterally has fought BLOOD AND SOUL back against to repress for so long.”
Think of it like this, your family and all you know held dear was killed by a pack of wolves. You tried to fight back, yet they kept killing your loved ones and livestock. They hunted you down relentlessly. You ran away with your people, over the seas to finally escape. You thought you were safe… Then the wolves came again, they killed more and your roots was again torn apart under teeth and claw. They didn’t only kill your kin, they played with them till their final breath - if they even were allowed the release of sweet death.
You don’t even try to fight, you already failed, so you run again. By miracle alone you get to escape again. You find allies that can help you kill the wolves, you join up - for the wolves did indeed come for you again. They never relented - but they got beaten back.
In the end you had lost all but the future. Your father, slain. Mother, tortured and maimed to the point of a destroyed mind. Your brothers dead, killed infront of your very eyes. Generations of loss. All you know is the fear of wolves. Yet, now you strive to build a world where the wolves can hurt noone ever again.
Would you ever forgive the wolves? Even more out of this world, would you let them into your home? I doubt it. Not after all the horrors inflicted.
Hopefully this helps you see why it is only logical that the Holy Fanatical Templars of unyielding resolve to fight the demon, would never allow the demon to fester within their own ranks. Would their Naruu really allow it?
A main character going 'It is fine guys, it is all right - they were only “tricked” to be evil. They good now" just doesn’t work - other than in an extremely naive world. The Naruu can just go “yes, let us manipulate the stuff of chaos and bend it to our purpose. Because that has worked so well in the past.” It makes little sense to a lot of us, based on what perceptions we got of how the characters work.
Yet, in the end - anything can be done. Nothing matters. Genocide is OK, just forgive them - take care of them. Of course, let us ignore that they are demons, that they litteraly feed and the anima of the soul and the magics of the world… what wrong could this do, other than open the path to yet another fall to corruption of the fell - that they personally just fought off a few years ago.
Yeah. It is what it is. It is like the Night Elves forgiving the Horde. It is because the gameplay experience trumps lore and there are no consequences in the fantasy setting of WoW. As mentioned, the Jailer and the Shadowlands made sure to make that clear. As such, when anyone points to a lore reason, just say this: Lore died a long time ago old’ man.