at the end of the day if all currencies crash gold and silver will still be worth fuck all
If they devalue currency to zero then what are you going to exchange your lumps of metal for?
That's sort of a dichotomy.
All currencies can't crash. People still need something to be used for trade simplicity i.e. a currency. in this modern digital world we live in.
Fiat currencies are sensitive due to manipulation by governments, also corruption and thus inflation.
That is what speaks strongly for Bitcoin, as a world currency. As it can't be manipulated, debased, inflated. And it's not impractical use of trade as means for everyday trade as gold or silver.