Answers from the SPSE – Catholic Apologetics Facebook group:
I’d say, “Are you sure?” and then I may add, “that could be true, I don’t know, I’m not God, but why would you want hamburger when you can have filet mignon?” Jesus, in the Eucharist, gives us His flesh to eat, and He said unless you eat His flesh, you have no life in you. That sounds like a big deal! That why we need to be Catholic. The Catholic Church has the true Eucharist. Why would anyone want to be without such a gift?
I would ask “Where’s THAT in the Bible?” If they give an answer, I’d ask them if their fallible interpretation. They will typically admit they are not infallible.
Jesus said, “Not everyone who says to me, ‘Lord, Lord,’ will enter the kingdom of heaven, but only the one who does the will of my Father who is in heaven. Many will say to me on that day, ‘Lord, Lord, did we not prophesy in your name and in your name drive out demons and in your name perform many miracles?’ Then I will tell them plainly, ‘I never knew you. Away from me, you evildoers!’
So, it seems to me that Christians won’t all end up in the same place.
I would remind them that at the end of our lives we’re all going to stand before Jesus and be judged on how we lived our lives. In the parable of the sheep and goats in Matthew’s Gospel, chapter 25, Jesus separated people based on whether they helped others or not. The people who fed the hungry, or gave drink to the thirsty, or welcomed the stranger and things like that inherited the kingdom of heaven. The people who did not do those things were sent away into eternal punishment. So, what saves us, ultimately, is putting the grace Jesus give us into action.