Infallibility arguments are mostly a waste of time. Oh, I suppose it's useful from a political perspective of suppressing endless battles within a denomination (do we need to hash out Arianism again? I didn't think so) but since the internet isn't an organization, infallibility on-line inevitably degenerates into a political battle over who "owns" the church (a subject I'll get to later).
When there's agreement, nobody cares about infallibility; it only matters if there is expression of doubt or outright disagreement. But in those cases it is ineffective as a defense of a line of argument. For the dissenter, the defects in the argument made are ipso facto evidence that the claim to infallibility is spurious. Thus, the recent attempts by some in the Vatican to claim that all papal bulls are ex cathedra infallible accomplish nothing except emphasize to outsiders how precarious some of them are. Most bulls which advance theological points do so through argument, and therefore are subject to the ordinary rules of rhetoric; the Vatican cannot really protect them from criticism, but can only refuse to listen.
The other point about infallibility on-line is that none of the usual respondents can actually claim it. I see no popes here, nor members of any magisterium. What we do is interpret what the (ostensible) infallible authorities say. These interpretations are not protected by infallibility by any standard.