Then you can give examples of that science fiction that we know can happen and why continue to consider it science fiction.
I can come back when I'm not at work and elaborate on it. However, since you're taking the affirmative stance, maybe you can meet your burden of why this should be the definition of science fiction. I think it is a bad definition. I don't think there is any logical underpinning to it. And I don't think it is followed by either science fiction publishers or authors. But if you want to make a case for it, feel free.