Try to understand that by making Bitcoin useless as a currency (buying coffee), you also destroy its value.
It has never been useful for buying coffee - so how can I be destroying its value for something that it has never been able to do well?
(it has been very useful to move money from one country to another with almost zero fees - so that has been something that I have not been able to destroy)
Bitcoin's value is speculative: people speculate that, some day, it will be used as money. they invest (gamble) on that becoming a reality.
Like they invest in *any* startup. Like they invest in a car company which is yet to sell a single car.
Don't assume that people will line up to buy your car company shares, not once the possibility of making cars is off the table.