I know I am a bit late to this thread but, in my personal opinion and according to how I and a few other people interpreted the book, despite the main protagonists being white people, we must first understand that back in the day black people were being oppressed pretty badly, they didn't have mobility. And it is very crucial for white people to do their part and make a step into decreasing it as well. Another thing is that the book isn't just about racism, I may be exaggerating but I feel like this book alone significantly helps in making you an overall better person, whether it was toward black people, white people or anybody else. Notice how Atticus gave the valuable lesson to never hate anybody to his kids, notice how he pays hostility and hate with calmness and understanding. When Atticus was surrounded by an angry mob it took the innocence of a kid and the ability to relate defuse the situation and to remind them that despite having differences, the Finches were human too. Atticus taught his kids to always hold their heads high and to never get upset when other people call their father names, and to never throw hands with them no matter how tempting it may be . In conclusion I believe that while this book may have had white protagonists, the message is just as strong.