I continue to hear many people with this theory. I'd be very interested in hearing the reasons for this theory. I still strongly believe that what happened to them on the island actually happened to them. For me, in fact, the entire emotional impact of the show rests on it. But I'll get back to that after I hear some defense of the "they were dead all along" theory.

*edit*
I just noticed that when I quoted you, I didn't know at what point you thought they were dead. Before the island, or just in the flash sideways?