I don't really give this argument much credence any more. If the value of, say, gold or diamonds were to drop their practical-use-floor-value, they'd be valued at probably less than 1% (maybe much less) of current value. I mean, how much gold is actually consumed by industry? And we even have industrial diamonds now.
A friend argued to me that crypto is "A Terrible Thing" because its just used to fuel the (illegal) narcotics industry. At this point, I'm doubting that too - the market cap of all crpyto, and the value being transacted e.g. daily volume, has increased massively recently. Are we to believe that narcotics have caused that? I can't imagine so - more likely to me it's around 90-99% speculation which, you might well argue, is "Another Terrible Thing."