The point of this is obviously that the USD is just as much as a construct as Bitcoin, which, sure! But of course the difference is that the dollar's value doesn't change by 20%+ in a day, so you can rely on it to execute transactions, sign contracts, set salaries, etc.

Bitcoin apologists have generally seemed to see Bitcoin's rise as a positive, which is somewhat true, but it has to be stable to be useful for ordinary people. A volatile currency is not a useful currency.