If you were to force people to do something against their free choice, you would be dehumanizing them. The option of forcing everyone to go to heaven is immoral, because it's dehumanizing; it strips them of the dignity of making their own decision; it denies them their freedom of choice; and it treats them as a means to an end. When God allows people to say 'no' to him, he actually respects and dignifies them.
