Just for the record: I believe in it, but I wanna try to explain why it still isn't confirmed. We can't rule out the possibility of WHH being wrong just because it would create a paradox (what some are explaining in the blogs with the grandfather paradox time loop). If the writer's really want, they could go with the alternate realities (universes, whatever you like) theory. That every action of a "future being" in the past, I mean every single one, not just the explosion of the bomb, creates an alternate reality from the previous one.
IMHO, that would be too confusion and less interesting than WHH. But my hope is that the creators didn't mean for any of the two, but a new, more interesting, way (where Desmond is involved).