Well, that's why I didn't say "blatantly false". There are often cases where someone has heard something so many times that they believe it's true (such as "Killing praying mantises is a crime in the US," or "Rice is no longer thrown at weddings because birds will explode," neither of which is true, or "Drinking bottled water is changing the Earth's climate," which is heavily disputed), and I would hesitate to call those people trolls. In such a case, a low karma on that comment and a quick rebuttal is certainly a fair response.