Krugman is right about a lot of things in this article, and wrong about one big thing.
He's right that Bitcoin (and generally, cryptos) do not serve any
mainstream purpose outside of speculation.
Satoshi created Bitcoin for one reason: to allow people who
could not use a normal bank to be able to trade numerically-delineated value. He absolutely did
not envision Bitcoin being used in a
mainstream way for everyday transactions, and the technical architecture of blockchain makes that impossible. Satoshi never meant to Bitcoin to be used by "everybody", or even a "lot" of people: the problem Bitcoin (and blockchain generally) solves is an
extremely narrow one.
Subsequent to Satoshi and his vision, however, many Bitcoin holders started ascribing things about Bitcoin that simply weren't true, and could never be true: that it could replace the US dollar or it could replace normal banks for mainstream everyday transactions.
Paul Krugman, like many (most?) who have heard a lot about Bitcoin but don't understand computer software architecture obviously believed this misinformation, and took it at face value that Bitcoin was "supposed to" do all of these things it has not, after 14 years, done.
Hence Krugman's conclusion:
All of which raises the disturbing prospect that an industry initially driven, seemingly, by libertarian instincts but which has never delivered on its economic promises will nonetheless be able to buy itself a huge government bailout.
In the context in which he is speaking, he's right about this.
But Krugman is wrong to say that Bitcoin serves no economic purpose.
Speculation is a valuable product, and one that has been in existence since human beings started trading with one another thousands of years ago. Bitcoin, as a meme investment, is useful for people, and will continue to be useful for people--as will meme investments in other cryptos, and other digital currencies.