Universalism is part of what brought me to Christianity, and the implausibility of universalism of it is part of what led me to stop being an active church-goer. Hell was one of the biggest issues I had with faith and religion, and Christianity in particular. When I realized there were Christians out there who didn't believe in hell, that is one of the things that made me reconsider an atheism I'd held since early childhood (It wasn't quite atheism, in some respects -- my view was that God probably didn't exist and if he did I'd disagree with him anyhow). I eventually became Episcopalian, where I held either a universalist or a semi-universalist (very few people are in hell) position for a couple years.
Unfortunately, I know longer believe universalism is consistent with the Christian faith. Don't get me wrong, there are genuine Christians out there who are universalists, but they're wrong about their religion, as best I can tell. Obviously, I could be mistaken. Everything points towards heaven and hell, though, scripture, tradition, history, and, in Roman Catholicism, the magesterium, and so forth. And everything points to both heaven and hell being populated.
One thing that's always kind of hard to handle, but I think is so true that it ought to be the starting point for any catechesis is: "God isn't whomever we want him to be, God is who he is". If there really is a God up there who is an objective reality, he can't just be a reflection of our individual mindsets. If everyone can invent their own god with attributes they completely agree with; they aren't worshiping a true god, they're worshiping themselves, or an imaginary god they've created in their minds. If God exists, we should absolutely expect that we'll at least initially disagree with a lot of his reasoning, and that it'll be challenging. If we automatically agree wholly and fully, isn't that a bit suspicious? "Oh look, by remarkably coincidence, God, presumably a perfect being with unlimited capacity for thought, is exactly like me, a random flawed human being with relatively limited capacity for thought, in terms of His reasoning and morality". Think about how implausible that is for a minute.
I'm not saying people should automatically worship this God because he is there. I'm not saying they shouldn't. But I do think it makes sense to search out who God is, to discover as much about Him as possible, and to make an informed judgment based on the objective reality of the situation to the extent one can determine it. If we just seek out or invent a version of God we can always easily agree with, that's not really God, in my view.
