Just as many who were brought up to think of God as a bearded old gentleman sitting on a cloud decided that when they stopped believing in such a being they had therefore stopped believing in God, so many who were taught to think of hell as a literal underground location full of worms and fire...decided that when they stopped believing in that, so they stopped believing in hell. The first group decided that because they couldn't believe in childish images of God, they must be atheists. The second decided that because they couldn't believe in childish images of hell, they must be universalists.