When did he say that? I don't want to put words in his mouth but I would guess more research needs to be done to ensure there are no side effects or unintended consequences... similar to what is done when medicine is developed.
the treatment being talked about falls in the medicine category. he is cautioning against it because the body doesn't do that already. let me rephrase that:
I caution against the use of cephalexin when your appendix bursts. if it was safe, the body would produce its own antibiotics.
I caution against neuron regeneration when your nerves are damaged. If it was safe, the body would regenerate its own nerves.
I caution against taking daily finasteride. If it was safe to not have ass cancer, your body wouldn't have ass cancer. thankfully in evolution, bald people don't reproduce as much, so someone bald and with ass-cancer won't pass on his opinions to the world as long as these awesome scientists.