"We are obviously irritated and feel a sense of ire at those who make such simplistic pronouncements and construe these to be indicative of a hackneyed view which shows complete disdain for the hurt and pain experienced by those from the former non-racial SARU SACOS rugby stable," the group wrote.
"While we do not wish to take anything away from your celebrated successes and greatly admired astuteness as a rugby coach, we do offer a word of caution … where rugby men start to venture on terrain such as pronouncing reasons for other countries' poor performance on a sports field."
As part of his research for the book Bills, a respected British journalist, had unprecedented access to the All Blacks during last year's tour by the British and Irish Lions.
Hansen's comments, which were part of a larger statement made of the Springboks, appeared to be a reference to the country's controversial - and divisive - quota system.
By next year's World Cup, 50 per cent of the South African team is required to be made up of players of colour. Many have suggested that despite the good intentions behind the system, it isn't necessarily the best for the national team in terms of being able to compete at the highest level.
"[Late former South African president] Nelson Mandela understood it better than anyone else," Hansen is quoted as saying in the book.
"He knew that the Springboks was a team that could unite the nation. I still believe it is, if they got things right and allowed it to develop naturally, it would. And you would get the right people in the team. In the end it would be a multi-cultural team.
"Rugby wasn't a black man's sport, but it was the sport that would unify the country in a way no other sport or business could."
The book, released in August, included claims from some former All Blacks that the haka has been over-used.
Sir Colin Meads and Kees Meeuws were among the high profile personalities to reveal their own frustrations about the heavy use of the haka. The team's mental skills coach, Gilbert Enoka, has revealed the All Blacks had previously felt "haka‑ed out" and some "hated" having to constantly perform the Ka Mate version.
All Blacks management declined to comment on the group's letter when approached by the Herald.