What does don't take advantage of people weaker than you mean? Or " don't kill mockingbirds" It's from the book To Kill a Mockingbird

In other words, "don't exploit the vulnerability." It is pretty self-explanatory to me so I am not sure how to explain though.

"Don't kill mockingbirds" basically involves innocence. Mockingbirds don't do anything harmful so it's immoral to cause harm to them.