Humans like to think they operate mainly using reason but the truth is we don’t give anywhere near enough recognition to the primitive brain and its effects on our emotions. It’s a rare story that succeeds even though the characters have nothing endearing about them. The scriptwriters of television shows such as Doctor Who and Red Dwarf are well aware of this. The reason these shows attract a cult following is the emotional roller coaster journey each character takes in the course of an episode, the incredible twists and turns in the plot, and the fascinating settings. The characters may be bumbling fools, self-seeking blamers, unbelievably vain, but if they show their emotions we can recognize elements of these traits in ourselves, no matter how suppressed or minimal, and so identify with their character.
If your bad guys are all bad, then they will come across as shallow cameos and if you’re not careful they’ll turn your story into a farce. If your reader has an inkling of why your antagonists are so nasty e.g., they were brutalized in their youth by bullies or parents, or they lived in a hostile environment, then they become more engaged with that character. When your audience identifies and sympathizes with your antagonists needs as much as they do the protagonists, then you can be sure your reader will keep turning the pages, especially if those needs are dire