These verses continue Moroni’s comments that were triggered by the text in Ether, but they are not directly related to it. The suggestion that when the Book of Mormon comes forth that there might be those who “contend against the word,” is a theme that both his father and he have previously discussed. Moroni’s focus is on the people who will receive this text, and this experience is the real spiritual message, it is the only place where there is a strong testimony of the Christ, in which is the message that most interested both his father, Mormon, and himself.
Thus, these statements about what will happen to the unbelievers refer to those who will not believe in Christ, not those who won’t accept the book of Ether as ancient.