The Empire was forced to ban Talos worship because they lost the Great War and it was one of the conditions outlined in the White-Gold Concordat. Many Imperials still secretly worship Talos. The book "The Talos Mistake" was either written to appease the Aldmeri Dominion or it was written by an anti-Talos person. The Thalmor didn't want anyone to worship Talos because he was once a man and the Thalmor could not believe that it would be possible for a man to become a god. For example, Elisif (the Jarl of Solitude) still secretly worships Talos, even though Solitude is the city most strongly allied with the Empire.
