It should be noted that BLAARGing involves the party(s) not actually believing that Bigfoot exists but instead pretending that it does as the theme for the role-playing. If a person(s) actually does believe in the existence then it is something other than BLAARG.
BLAARGers are something like American Civil War re-enactors. They don't actually believe that they are fighting soldiers in the Civil War - they are only engaging in role-playing to simulate that they are. They enjoy it. It's a hobby. A pastime. Sometimes it's an obsession that absorbs lots of time, effort, thought and money.
Above all, the important endeavor of the BLAARGer is to convince the audience that they truly believe instead of only pretend to believe. The primary goal is not to convince you that Bigfoot exists, but rather to convince you that they believe (or are certain/know) that Bigfoot exists.