"According to what i read up on in the past and present regarding Him, Mainly for power, to be the chief God of Egypt, and cutting him up was so Osiris could not be resurrected. He was Originally a God of disorder, a trickster sometimes and the God of foreigners and he has good aspects to himself like protecting Ra from Apep, however he was mainly villainized in a similar fashion to the fae being associated with 'demons', when Egypt was conquered by foreign nations, and since he was the God of foreigners he was pointed the blame that the foreigners brought problems and oppression to the land, and Horus who had won Egypt over Set-h (they were supposed to have a race of stone boats to a finish line but while Set followed the rules and his ended up sinking, Horus the son of Osiris actually had a wooden boat painted to look like stone so he won, but he already had the title over Egypt won before the race anyways) was celebrated more. Then the Gods were associated with Good and Evil and things became different. :o"