Which side are you arguing here? And how does papal infallibility follow from god's assumed properties? After all, he (the pope) is still human in all other essential ways; even the RC spin doctors are apparently reluctant to make so bold as to suggest differently.
What were the sides again? Seriously, though, what I meant was this: Catholics believe that Christ promised that the Church would be preserved from serious (dogmatic) error. The properties of God (as viewed by Catholics) logically imply that such a promise can and will be kept. Since the nature of the Church is such that a false
ex cathedra pronouncement from the pope would result in a violation of God's promise, it follows that God will not permit the pope to make an
ex cathedra pronouncement if it would be a false one. What's driving that putative outcome isn't the qualities of the man in Rome; it's God's supposed properties of truthfulness, power and so forth. Such a God could prevent the pope from making a false
ex cathedra statement of faith in any number of ways that would not confer any superhuman wisdom or insight on the man himself; accordingly, nothing about the doctrine of papal infallibility
per se requires anyone to think there's anything superhuman about the pope - just about God.
Still working from the Catholic perspective for the sake of argument, let's suppose that the pope were the sort of person so ignorant of or indifferent to God's will that any
ex cathedra statement he made would be either wrong, or else right only by sheer lucky guess. Such a pope could still be infallible within the meaning of the doctrine of infallibility, because God could either prevent him from speaking
ex cathedra at all, or else let only the lucky guesses slip past the pope's lips. That wouldn't make the pope deserving of any special credit, but it would leave Christ's promise intact.