There is nothing peaceful about the premise. The premise is “the worst evil first, after that, we’ll see”. And it is supposed to lead to conflict sooner or later. Just not the usual “the world will end, if we don’t exterminate them all now” kind of conflict.
Yes. And it seemed there were no enemies left that were more clearly evil. So I really don’t see the situation as comparible. The long-term goal would still be total domination and cultural homogenity. That’s what makes them the enemy faction. But in the short term the goal of getting rid of evil and prevalent death, void and fel magics that plague Azeroth makes them the enemy of our enemies first.
No one has to be fooled by it. They just have to be - dare I say it? - pragmatic about it. And not even all of them, just a relevant majority.
And about fanatics being unreasonable in nature… that may be true for our world, where no god was nice enough to make itself scientifically provable, or to send its angel-equivalents again where we can all see it. But in WoW? The Light is real, and it can bring enforced harmony that does seem to feel well enough. Being willing to go for that isn’t necessarily unreasonable. It just prioritizes contentment over freedom.