I'm not even sure why he's considered evil, to be honest.
Basically his entire backstory is:
"Hey dudes, the gods are lying to you. They say they grant spells, but actually they do jack shit."
"OMGWTFBBQ YOU LIAR..." *snicker-snack*
"Oh... wait, he was telling the truth. Screw you guys, I'm joining up with team Not-Lying-To-The-Entire-Cosmos"
"HERESY!"
Well, actually that *snicker-snack* should have been the first line, since he apparently saved that secret for his dying words out of a sense of misplaced drama, but whatever.