What a wretched, vulgar Frenchman can teach you about having faith in your ideas — Everyone loves a juicy spat. (And spats don’t come any juicier than the Trump/Biden September slanging match). But take a look behind the mud-slinging, slurs and insults and you’ll usually find two groups — the galvanised and the petrified. The galvanised understand that everything has changed. The galvanised are driven…