Let’s start with a truth that rules many an author’s writing: villains make the world go around.
Protagonists without antagonists are vanilla sundaes without toppings; they’re there, they’re okay. They’re good for a quiet night alone on the couch. But in the end, you’ll feel mildly disappointed that there wasn’t something more exciting filling your bowl. Without “the bad guy” gracing your pages, how does the story grow?