We don't really know if Orgrim would've prosecuted genocide against Humanity or not - based on his personality I'm more inclined to say not. Unlike Blackhand it's more likely he would've opted to break Humanity's ability to fight the Horde and pushed them out of whatever lands the Horde wished to claim, but would not have chased them beyond that. Of course, given the Horde's general corruption by the demons this may not have been within his ability to choose, either. Orgrim was not himself corrupted by Mannoroth's blood, and had also become aware that the Horde's crusade was based on a number of falsehoods. But his control over the corrupted Horde was not absolute, either.
This sounds like a judgement made from your own personal reference point and not one internal to the narrative itself - you're judging Orcish culture based on real-world human norms. In that sense I'd agree with you, it's a very bad culture and replete with a number of problem elements. But you're also judging Thrall by a pretty unfair standard that could never realistically be met by the Horde in their own context. I've already said that the Horde needed to acclimate to a world that wasn't as savage as their homeworld of Draenor, but I don't hold them to the same standards as I do our own society in the real world.
Where do you think scholars came from historically? The scholastic concept was born out of figures like the shaman and the priesthoods of various mythologies. The Legion is well known for corrupting societies even more refined and evolved than the Orcs, as well, I mean the Draenei themselves were deceived and corrupted easily by Sargeras almost en masse - that's not a fair comparison at all, and Kil'jaeden was even able to manipulate the Orcs by masquerading as the very real spirits of their ancestors. And some Orcs still resisted his words despite this, which I don't put under the heading of "easy" at all.
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I don't think I'm apologizing for the Orcs at all - considering I've already said their culture has issues and hasn't properly acclimated to a world where they don't have to be defined by conflict. Orcish culture still bears responsibility for giving rise to personalities like Garrosh and Grom to begin with - they don't define all Orcs, but they're still a product of the problems of Orcish culture to begin with.