That goes against everything the game has been trying to convey.

Everyone goes on about how they want DLC to save Asriel, but no one ever talks about trying to save Chara. Don't you find it odd that they have such a hatred towards humanity? What could have affected a child so badly that they want to kill a village full of people?
If he wanted to kill everyone in the world, why did they make Asriel leave the barrier to kill humans, when there were monsters right next to them? Could it be that they actually found companionship with them, until Asriel, the best friend they've ever had, "betrayed" them, leading them to feel as if there was no reason to let anyone live anymore?