For the record, I hate this out-of-hand dismissal of anyone who asks "What if..." about anything outside the current Overton Window.
What in the world is an "antibeliever?" I find it kind of telling you chose this phrase instead of anti science.
For example, people who say Bigfoot or aliens are absolutely not real and anyone who believes in such is clearly a loon rather than saying "It's unproven and seems extremely unlikely."
maybe they should be called a firm believer, then?
like, in science?
the opposite here is the default until you prove your thing true and the default false