A lot of those books received a complaint by some parents or were maybe even possibly removed from a school library in one of the thousands of schools in the US. That's what they mean by "banned." It's just a way to market approved books to kids who have to read them anyway as if they were edgy.

In TKAM's particular case, a lot of the complaints came from across the spectrum because of the use of racial slurs, so it was often not even controversial for the reason you might think. Frankly the book is not even good outside of its propaganda value for fighting racism. At any rate, even then it wasn't meaningfully a "banned book", even in the south.

https://www.pbs.org/newshour/education/to-kill-a-mockingbird...

Sometimes "banned" is a complete misnomer, as when back in 2017 it was simply removed from the required reading list in one Mississippi school district because people complained about reading racial slurs out loud. But the reporting, as you can see from Google, almost all says "banned."

If you want to ban a book that deals with racism in a meaningful way because you are actually for the racism, this is the argument you would make in public.

Reading racial slurs and understanding how the character felt and feeling bad about it is the entire point. If your only exposure is casual racism on the worst parts of the internet then you just normalize that way of thinking.

I will fight anyone that says To Kill A Mockingbird isn't good.