Philosopher Karl Popper said that for an assertion to be scientific, it must be "falsifiable." In other words, some evidence could appear at some point to prove the assertion untrue. When someone says that Diet Coke erases your memory, it might be stupid gossip, but it's at least falsifiable, which is why those kinds of arguments tend to die quickly. On the other hand, when someone makes the kind of argument that can't be proved or disproved, they're not simply being dishonest but their assertion tends to spread like cancer among those who can't employ simple insight to stop it.
The main thing is to avoid the arguments by calling bullshit on whoever uses them. So steer clear of anybody who ever says stuff like this:
--*The current economic crisis was caused by homosexuality and abortion
--*Human wickedness, particularly sex and violence on television, caused 9/11
--*The ice caps are melting because we offended God by not honoring Him daily*
--*Our whole synagogue is being punished because somebody dropped the Torah*
--*Nazism was caused by all of us being less Christian
--*The Rodney King riots were caused by the legalization of abortion
--*The Kennedys are cursed because their family patriarch made his money dishonestly
--*The United States is a fascist theocracy
--*9/11 was a conspiracy
--*JFK's murder was a conspiracy involving lots of people who are now dead and who can't confirm it, so we just have to assume it's true
--*Strawberry Shortcake is a demon from hell*
--*Tinky Winky is gay
*With the exception of those things in asterisks (which I got from literature or from flight of fancy) all of these things I have plucked right out of the media by various dunderheads, blockheads and mouth-breathers. Most, but not all, are right wingers, natch.