I think its important that racist books or books containing racism should be published. Racism is unfortunately a part of our global community, and people need to be made aware of it. Sometimes reading a book that portrays something like murder or rape in a favourable light really repulses people and this is an important mechanism. It keeps us aware that racism is an ongoing issue.
If racist novels were censored, would it then be neccessary to censor television shows and movies which depict racism? In this case, it would appear on the surface that racism had gone away, but it would just not be something that was in the public eye anymore.