Searching for more information on it, I found this list of classic novels that have been challenged in the past. It also give information about the reasons they were considered objectionable:
Great 20th Century Novels Targeted by Censors
I really do believe that art creates a safe space in which we can discuss and analyze the ideas that speak to us, even those that make us uncomfortable and perhaps offend us. In that safe space, we can observe the world around us as it's seen by our creative peers, and, holding those thoughts and ideas up in our minds against what we know or feel to be right, we come out as strong-minded individuals, better for having examined so many possibilities.