To Kill a Mockingbird talks about things like rape. People had more objection to the issues of incest and rape than they did of the rampant racisim and treatment of black people.

A Wrinkle in Time is considered antiauthoritarian and anything with a fantasy theme is considered the work of the devil by evangelical religious groups.

Little Black Sambo is considered racist by a lot of hyper liberal groups. Mind you these people have no sense of context. They also don't like Mark Twain for the same reason.