I just learned a fun new etymology that I wanted to share. The word villain actually comes from the Latin villānus, which simply meant someone who lives on a farm or country estate (like the word villa). So how did it come to be the word villain as we understand it with its modern meaning and negative connotations? Well, thank you for asking. It was from the point of view of city-dwellers!
If anything is going to convince and/or remind you to write complex “villains” with actual, relatable, and understandable motivations, then it has to be this etymology. It’s just the perfect reminder (or, at least, it was for me) that readers may only experience a story through a certain lens—omniscient narrators aside.
Maybe the conflict between the protagonist and antagonist in your story simply comes from a fundamental misunderstanding of each other (like city vs. country). Or maybe your antagonist is truly evil (whatever that means in the context of your story). That’s great, too, as long as the characters all have the proper backstory and desires to motivate their actions, even if you as the author are the only person who knows them.