Now I am a person who is really interested in how story structure works and I think that an antagonist AKA the main villain is a truly important aspect of a story. Without an antagonist, there is nothing in the protagonist's way to make what they need to do easy, and it's hard to give a story high stakes at all without one. Now I might be murdered for saying this but, I never really liked the movie "My Neighbor Totoro" for specifically that reason, it lacked a villain, a true threat, the only high stakes were at the end of the movie where Mei gets lost. The movie just bored me to death for a good chunk of it because most of it is "Oooooh big hapi majik bunni thiingy majigy" and no threats or high stakes. So I believe any good story needs an antagonist.