Gray Area, the objections you list are objections from within a model. This is right and proper. A lot of people don't reason the same way you do, though. Quick replies: (1) We know from sheerly physical considerations that you can build a brain at least a million times as fast as a human brain, which gives us many interesting results of itself. (2, 3) Barring a specific model of cognitive science one cannot disprove a magical upper bound which lies exactly above human intelligence, even though raw evolution encountered no apparent difficulty in accidentally building humans out of chimps using only a threefold increase in brain and a sixfold increase in prefrontal cortex. But the principle of mediocrity weighs heavily against such an arbitrary presumption, as well as the general notion that evolution doesn't build optimal systems, plus all the known flaws we talk about on Overcoming Bias. Furthermore my own, specific model of cognitive science is already suggesting that we can go beyond human purely on the basis of writing better software, but this is too complex to justify in detail here - the common sense of this should be apparent, though.

Doug, it may help to think in terms of a log odds ratio, in which case a probability of zero corresponds to negative infinity. You could never get that much counterevidence - we are talking about a subjective probability, not an objective frequency. Perhaps you are hallucinating or deluded or a toy in a computer simulation of mathematical error. Infinity is not a number, and 0 is not a probability.

Jonvon, there is only one human superpower. It makes us what we are. It is our ability to think. Rationality trains this superpower, like martial arts trains a human body. It is not that some people are born with the power and others are not. Everyone has a brain. Not everyone tries to train it. Not everyone realizes that intelligence is the only superpower they will ever have, and so they seek other magics, spells and sorceries, as if any magic wand could ever be as powerful or as precious or as significant as a brain.