I should qualify my statement. I was talking only about the common varieties of utilitarianism and I may well have omitted consistent variants that are unpopular or weird (e.g. something like negative average preference-utilitarianism). Basically my point was that "hybrid-views" like prior-existence (or "critical level" negative utiltiarianism) run into contradictions. Most forms of average utilitarianism aren't contradictory, but they imply an obvious absurdity: A world with one being in maximum suffering would be [edit:] worse than a world with a billion beings in suffering that's just slightly less awful.