You think heliocentrism was defined heresy and/or contrary to defined doctrine, right? But you have apparently no difficulty with the Church saying a Catholic can defend [what you think is] a heresy in print?

1820 is about 200 years after 1616. It hasn't quite been 200 years since the Immaculate Conception was defined, but are you really saying the Church could say that it's OK to formulate arguments advocating the contrary, and print them in books, with the proviso that of course he does so at his own risk? That it is only an opinion, even if the author believes the contrary of the Immaculate Conception to be fact?

Finally, If St Thomas can use the thoughts of a Pagan that reflect truth, then I will use a truth uttered or written by a Pagan also. Nor do I consider all non-Catholics as 'enemies of the Church' as you do, not even atheists. But the above does tell me you are a helio, so no wonder you do not like what you are reading.

Can it be said that either Paul V or Urban VIII so committed himself to the doctrine of geocentricism as to impose it upon the Church as an article of faith, and so to teach as pope what is now acknowledged to be untrue? That both these pontiffs were convinced anti-Copernicans cannot be doubted, nor that they believed the Copernican system to be unscriptural and desired its suppression. The question is, however, whether either of them condemned the doctrine ex cathedra. This, it is clear, they never did. As to the decree of 1616, we have seen that it was issued by the Congregation of the Index, which can raise no difficulty in regard of infallibility, this tribunal being absolutely incompetent to make a dogmatic decree. Nor is the case altered by the fact that the pope approved the Congregation's decision in forma communi, that is to say, to the extent needful for the purpose intended, namely to prohibit the circulation of writings which were judged harmful. The pope and his assessors may have been wrong in such a judgment, but this does not alter the character of the pronouncement, or convert it into a decree ex cathedra.

The difference is that the non-Catholics in this case do not reflect truth. The atheist was reflecting false objections in the field of theodicy (the part of philosophy dealing with the existence of God), yet that's the specific point you endorsed. The heretic was denying an unambiguously defined doctrine of the Church (after it was defined), yet you brought him in as if he was an authority on that very doctrine.

I think the framework of your view makes way more infallible (or "irreformable") statements than even conservative theologians writing after 1870 think. I happened to check the Galileo affair in the old Catholic Encyclopedia, and it says the Index can not define doctrine. (This is much more fundamental than your arguments about who signed what.)

I say that if a real proof be found that the sun is fixed and does not revolve round the earth, but the earth round the sun, then it will be necessary, very carefully, to proceed to the explanation of the passages of Scripture which appear to be contrary, and we should rather say that we have misunderstood these than pronounce that to be false which is demonstrated.

Second, as I just noted, the 1616 assessors report covered two propositions, but only one was evaluated as contrary to Scripture, namely the sun's rest and centrality. Current science happens to coincide on rejecting the sun's rest and centrality.

I don't think it's binding to begin with.

But even Ineffabilis Deus, in addition to the Immaculate Conception definition properly speaking, has a lot of other text giving explanations and so on. That Church is not "irreformably" bound to the other text.
Rev. Roberts book was published in 1885, after papal infallibility was defined.  The intro to the version linked above says he denied infallibility.