Personally, I have a hard time seeing emotions as "all bad" or "all good" - Even hatred has its good points occasionally, and can be turned to good ends. If you "hate" injustice for example -- people usually don't think of that when they think of "hatred," but if people don't actually, truly, literally detest, despise and wish to see an end to injustice, justice will not happen for them. More dubiouusly, there are survival stories out there of people who survived impossible odds simply because they were after an enemy or felt a friend had betrayed them and their *burning hatred* gave them the will to keep on going until they were able to get out of the situation. For me, hatred is evil when it has certain targets or a certain bent - irrational hatred, hatred toward people of a certain race, creed or sex just for existing, ect.
And that's what I think Demise had - a hatred for the Goddesses and their people, so he had the bad kind of hatred. Still, that hatred must have been fueled by other things - anger, for instance (which likewise can be good or bad, depending upon use), perhaps even a Well-Intentioned Extremism (creating a world only for demons, only for the strong).
I have developed an idea about Hyrule that the "monsters" of the land are actually born of human emotions and desires - that the land has a kind of magic in it that gives shape to some of the things that are in people's hearts and draws them out. Their irrational hatreds and overages of negativity and greed become the shadows they fight with swords. In this way, most of the people of Hryule are actually pretty good people, rather kind - I mean, everyone in the villages is so nice and helpful most of the time! I'd love to live in Hyrule! I think that Demise, quite possibly, is the ultimate of that "coeleascing hatred separated out from people." In other words, while in our world, we have these gray-moraled wars with terrorists and nations of differing interests, but it all ultimately involves human beings... and in our world, while we have Hitlers... Hyrule gets Demise/Ganondorf and wars against monsters with more-or-less black and white morality.
If any of the "rest" of Demise is reincarnated, I think Ganondorf has his hatred, his virility (Gerudo harems!), desire, and maybe even just a little bit of love and joy - of the kind that wants to take the beautiful things for himself and no other.