it’s not that gon actively hates himself (at least for the majority of the series – it’s arguable that at several points in the chimera ant arc he is practically drowning in self loathing, and That Scene (”i should have died instead”) in the election arc springs to mind as well)
rather, he doesn’t value himself. he doesn’t see himself as worth much – sure, he’s okay, he’s mostly happy most of the time even! but he’s not much to get worked up about (in his mind) and so the idea that other people would risk themselves trying to help him is unpalatable and confusing to him.
i think the only time that this sort of less obvious self-worth issue doesn’t crop up and keep him from allowing someone to make a sacrifice for him was in the dodgeball match, and i think there’s more than one reason for that.