If you are absolutely clueless about a subject and have absolutely no facts to form an opinion with--your opinion is fantasy because it isn't based on anything but your imagination.
AN OPINION IS YOUR PERCEPTION OF SOMETHING. A FACT IS REALITY. IF YOU TRY TO PASS YOUR OPINION OFF AS FACT... IT BECOMES FANTASY. STATING A FACT IS NOT ABOUT DISAGREEING WITH YOU. IT IS ABOUT YOU NOT HAVING THE FACTS AND WISHING SOMETHING ELSE WAS TRUE. THAT IS FANTASY.