I chalked it up to him distroying a town and causing the deaths of a few thousand people being a sobering experience. I mean the party was telling him he was an awful person and then he looks at himself after Akzerieth and goes "holy crap they're right." Then he decides he needs to change himself. Of course he takes it too far, and that's constantly pointed out to him in the game. By the time he gets to Eldrant or whatever he's become a lot more reasonable person, I thought.
So it's not very subtle but I didn't find it completely unreasonable.
TotA's plot is kind of hit or miss, though. There's plenty of people on B8 who don't like it.
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