I'd expand on that question a little bit:

How about you prove that it isn't? (vary this question depending on which idiotic statement has been made). Please provide sources- My sources (list them- company IR, Idaho Geological Survey report, etc.) say your statement is false. And I will believe official and reliable sources over an anonymous poster any day, especially any poster with a history of stating "opinions" with no support that contradict every reliable source.

Call them out for what they are. They are either ignorant of or purposely ignoring available facts and information. If they can't provide a reliable source to back up their statement, then they are just yet another anonymous poster on a message board with a dismal track record of false statements and failed predictions. (Be sure and do it within the "TOS", though!)