I think that because Hurley was with Locke, something bad is going to happen. Maybe it is Hurley who is responsible for Claire's death as well as countless others on the island. If by being with Locke somehow leads to his accidentally putting many in harm's way, he would definitely feel responsible. Or maybe it doesn't go as far as death, but just causes Jack a lot more trouble in the long run. I don't know what it could be yet but maybe there is a conflict between the two sides (Beachies vs. Townies) and things go badly from there. Being on Locke's side might mean facing off with Jack.