Only up to her
Most things in the world aren't black, aren't white, aren't wrong or aren't right. The wrong thing could be right in its own way and the right could be wrong if spun around.
The other meaning of what Callum said could be inferred in a way that Santiago was neither an evil nor a good character, he was just a grey character trying to be the Villain and was succeeding to a certain extent.
"What if he was a hero?" Callum then asked her. Before Persephone could open her mouth to answer, he continued, "If he was a hero, all his deeds which are called sins would be justified just because is a hero. A hero's deeds are never called sins. Doesn't matter if he killed thousands to avenge one life. He is still the hero. Why? Because we gave him the name of a hero." His soft gaze fell on her pale face as he added," Santiago called himself Villain because he believed he didn't deserve redemption or he was beyond redemption."