The human and the p-zombie are distinguishable because one is in the zombie universe and one isn't. For the purposes of the experiment, you're not supposed to be able to tell which universe is which by observation of the universe itself (i.e. there is no property of p-zombies that gives them away as p-zombies), but from the outside looking in I guess you have a label for one and a label for the other.
Like I said, it doesn't seem germane to the thought experiment anyway, which doesn't allow for epsilons, at least none that could have a causative effect on anything. Like, if you have universe A with no consciousness, and universe B with orange-flavored consciousness, and universe C with grape-flavored consciousness, and finally universe D with cherry-flavored consciousness, and none of them are distinguishable from the others except for universe A and universe D, then you're violating the terms of the thought experiment because you have two supposedly physically identical universes which are nonetheless distinguishable by dint of their underlying consciousness substrates (or lack thereof).
Anyway you're right, it is a weak argument, but only because it doesn't go far enough in outlining why p-zombies are ridiculous (which, IMO, the argument I presented instead, does).
Like I said, it doesn't seem germane to the thought experiment anyway, which doesn't allow for epsilons, at least none that could have a causative effect on anything. Like, if you have universe A with no consciousness, and universe B with orange-flavored consciousness, and universe C with grape-flavored consciousness, and finally universe D with cherry-flavored consciousness, and none of them are distinguishable from the others except for universe A and universe D, then you're violating the terms of the thought experiment because you have two supposedly physically identical universes which are nonetheless distinguishable by dint of their underlying consciousness substrates (or lack thereof).
Anyway you're right, it is a weak argument, but only because it doesn't go far enough in outlining why p-zombies are ridiculous (which, IMO, the argument I presented instead, does).