A large part of the issue is that the definition of lashon hara depends on your values. So when you have one major publishing company printing almost all of these “biographies”, it appears as though all the gedolim consulted with the CEO of that company, since anything he would have thought was “wrong” by definition is excluded from the book. Also, the people who are vocal supporters of censoring books tend to share certain viewpoints as well, so even publishers who would be willing to print with another viewpoint have an incentive to keep things as vanilla as possible.
Menu