If I understood Hansen correctly, he argued in his book about the first 500 years that though Justinian was incapable of suppressing universalism, he did contribute significantly to its demise:
he [Justinian] arbitrarily closed the schools in Athens, Alexandria and Antioch, and drove out the great church centers that theological science that had been its glory. He had “brought the whole empire under his sway and he wished in like manner to settle finally the law and the dogmatics of the empire.” To accomplish this evil work he found an aid in Rome, in a “characterless Pope (Vigilius) who, in gratifying the emperor covered himself with disgrace, and jeopardized his position in the Occident.” But he succeeded in inaugurating measures that extinguished the broad faith of the greatest fathers of the church. “Henceforth,” says Harnack, “there was no longer a theological science going back to first principles.” (www.fysis.cz/filosofiecz/texty/universalism.htm#292)
Hansen of course mentions other reasons why universalism almost disappeared. To me he seems to place the greatest emphasis on moral degradation of the church that didn’t care about people anymore and became more “practical”. I don’t reject that argument, it might be true. But I think it’s a claim that’s hard to prove and opponents of universalism will probably brush it off. Actually, I even read somewhere a kind of an opposite argument – that because morality was going down-hill theologians realized how naive universalism was. Now I don’t buy that argument, all I’m saying is that connecting a moral decline with condemnations of universalism and saying that universalism was condemned mainly because the majority of clergy were suddenly bad people is problematic.
What I think we’ve been discovering in this discussion is how complex and nuanced the development of ancient Christian views on hell was. We can’t fully explain what happened by pointing to Augustine, Justinian, and corrupt popes. I would add to the list of the main “culprits” Chrysostom whose frequent proclamations of endless hell influenced eastern Christians, but even so the development that took place is still very far from being explained. There were numerous individuals who played their part in suppressing universalism, they could’ve been simply corrupt, or just genuine admirers of Augustine and Chrysostom. In the west it was for example Fulgentius of Ruspe and Gregory the Great (both of these not only believed in endless torment, but even fully accepted that all unbaptized children will experience it, Fulgentius even wrote in To Peter on Faith that Christians should never doubt that even unborn miscarried babies must burn). We should also not forget Cyprian and Hilary who actually came before Augustine and advocated endless hell in many places. In the east I could name off the top of my head only John of Damascus who lived in the 7th/8th century. Here’s one quote of his:
everlasting life and everlasting punishment prove that the age or æon to come is unending. For time will not be counted by days and nights even after the resurrection, but there will rather be one day with no evening, wherein the Sun of Justice will shine brightly on the just, but for the sinful there will be night profound and limitless. In what way then will the period of one thousand years be counted which, according to Origen, is required for the complete restoration? (www.newadvent.org/fathers/33042.htm)
Now all the people mentioned were quite influential, but there were certainly many others who had a hand in this. Plus the doctrine of reserve, medicinal lies, purgatory (that could explain away references to the purifying fire), so-called Nestorians who were universalists separating from the imperial church, and a couple more factors… and maybe when we add all that together we’re getting close to explaining why things turned out as they did. So although I’d say Justinian played an important part, he was just an individual and no individual could single-handedly turn the tide. I mean, even if Augustine (who is perhaps the one most culpable for the spread of endless hell) didn’t attack universalism, endless torment may have still triumphed. It’s not like Augustine had significant influence in the Greek speaking world, and yet endless hell came on top even there.
I don’t believe Jesus was resurrected so I certainly don’t view myself as a Christian. I also am not a materialist because I don’t see how my mind could be material. And perhaps there is a conscious god who created our minds and is somehow always present in them.