The red herring is the implication that people spending fiat currencies are not making silly choices when they choose to spend them and that people spending btc are making a silly choice.  But that masks the reality that people spending fiat are making a choice not to buy bitcoins.  The price of bitcoin is going to do whatever the price of bitcoin is going to do.  At any point in time, you have a specific amount of stored value in currencies.  Which currency they are in at that instant is irrelevant.  You make a choice on what to do with that stored value based on quite a few variables and then tomorrow you have a different specific amount of stored value.  If I buy a pizza today, does it matter if the currency is USD, EUROS, or BTC?