I tried to get at it before, but it really just comes down to this: there is a difference between lacking a belief in something and positively asserting that something does not exist.

I can lack the belief that breaking a mirror is seven years bad luck. Millions of people who have never even heard of the superstition are do just that. But that is different from asserting that breaking a mirror does not lead to seven years bad luck.

Not asserting something is different from asserting its opposite.