What are the drawbacks of censoring certain information in history books?

Where does it all end - sanitizing history does nobody any favours in the long run. History is written by the victors and is rarely objective - you need to consult many sources in order to get a better perspective. If you look at the reporting of 9/11 for example it is still unclear as to exactly what happened - imagine trying to get clarity of events 300 or a thousand years ago.