to which the best response is to give up and walk away, if the person is arguing from a fundamentally different set of precepts FGA or no there's no point.

that same person could also argue that their position is true because Kermit the frog has decreed as such.

The insidious subtly of FGA's is that in a rational argument between sensible people an FGA can be used without anyone saying things which are obviously untrue or obviously stupid/insane. It's simply that an FGA is so broad that either side could use the FGA and have it feel like it supports their position.