It would be particularly good to hear from Catholics or Orthodox Christians because we don't often hear their views on this subject. If you're Protestant, like me, and you'd like to contribute, would you please only give what you believe is the established view of your denomination, if it has one, rather than your own personal viewpoint.
I'll kick off by quoting a couple of, admittedly pro-universalist, views by members of the Catholic and the Eastern Orthodox church that I read recently. It would of course be good to hear any viewpoint, whether that's pro, anti or neutral.
EO representative:
"There's no issue with Universalism in Orthodoxy, it's a permitted view. At least one of the Cappadocian Fathers who are highly revered in our Church, St. Gregory of Nyssa, was an avowed Universalist, and the theologoumenon of St. Isaac the Syrian is very convincing on the subject!"
Catholic rep:
"Catholics can believe all will be saved. We believe that "hell" as a state of rejection of God's love is at least theoretically possible; but there's nothing that says we have to believe anyone will be in that state.
Pope Benedict XVI wrote in Spe Salvi about how most people have an underlying openness to God, and "our defilement does not stain us forever" as long as we continue to reach out toward God.
It's a teaching of the Church that mitigating circumstances can reduce personal culpability for sin; and "mortal sin" actually requires 3 elements which include full knowledge and full consent, but it's not infallibly defined what those specifically mean. So along the line's of DBH's reasoning, I would say that since it's irrational to reject God, it's possible that no one is actually, in the right mind, intending to reject God as God truly is.
As others noted, Pope Francis has encouraged Fr. Richard Rohr, whose teachings strongly imply universalism and Pope Francis has straight-up said "the Lord has redeemed all of us, all of us, not just Catholics, everybody!""