For hypothetical example; Father/son duo are criminals, harming, killing, and stealing innocent civilians. Superhero fights them, resulting in the father dying. Son is now portrayed as a sympathetic villain because all he wants is to avenge his father... despite all the fathers of children they murdered whilst comitting crimes.
Side question; do you feel sympathy for the villains portrayed like this?
When it's done right, it's thematically about how violence begets violence, or maybe the writer is making their rivalry more personal. Without specific examples to dissect it's impossible to make that call though