My response: First off, while heavily implied, Ten feared death because he’s actually experienced it (and his personality was one which wanted to cling to life). His memory is what carries over from previous incarnations. In short, he remembers each time his body regenerated. In death, even The Doctor goes through deconstruction (physical death) and reconstruction (birth). A cycle we, as humans, only experience once. That’s is where the disconnect lies…and as humans, in a linear timeline who only live one life. We die and that’s it. For The Doctor, he dies over and over again then rises like a Phoenix (most likely the inspiration for his energy expulsions). Why each incarnation knows death is due to the memories of past selves and the trauma, both mental and physical in each grueling demise. As for the First and War Doctors, old age had arrived; the latter could let go of himself because he finally stopped fighting and found peace. Ultimately, no matter how The Doctor appears, he is NOT human.
Also, I would [agree with the first theory]. I think there’s little reason to question it. However, there is so much left open that I can understand an observation like this. This article is well written and it did make me think (despite my disagreement with the premise). Well done!