You could agree with this title and still want to buy bitcoin, because even if it were true that bitcoin has little shot at ever being a major global currency,

You could agree with this title and still want to buy bitcoin, because even if it were true that bitcoin has little shot at ever being a major global currency, the expected value of owning it could still be higher than the current price. If bitcoin became a major global currency its value could easily be 100x what it is now, which means there only has to be a 1% chance of that happening for it to be worth buying.