Perhaps I'm misreading the parent, but I think he said "to Kill a Mockingbird" was one of the first required readings in school that did not fall into the drivel category.
Second, even if and when we reach a point in society where racism is truly gone, it is useful to know how we got there. To Kill a Mocking Bird not only helps show how society was before, it was itself a small piece of history that helped in a small way make society the way it is now with less racism.
Even if we reach a utopian day where its lessons are no longer relavent (and we are not there yet), it will remain a significant aid in understanding our history.
Racism, in the first world other than the US, seems not dead but mortally wounded and we are ready to move on to the next problem to tackle.
I can't comment on the dryness of TKaMB though I would say that it does contain enough elements of typical human drama to be more than "a book about racism".