IF not believing in something is a belief system, then.....
Not believing in Santa Claus is a belief system.
Not believing in ancient aliens is a belief system.
Not believing in elves or fairies is a belief system.
Not believing in Big Foot is a belief system.
You are not allowed to not believe unless you develop a complete belief system. Oh wait. That could lead to dangerous mind-control cults. Too bad. Not believing is only allowed if it is a "belief system."