There are fair criticisms of BTC here. However the author is confused if he assumes that Austrian economists are not critical of BTC. Allowing Krugman to define what libertarian views are is suspect to say the least.
Mr Krugman is just one voice in the collected "Yes, Bitcoin is a Ponzi" articles. As you surely know - the most outspoken economist on the bitcoin investment fraud / bubble is Mr Rubini. See this US Sentate testimony, for example, https://bitsblocks.github.io/crypto-bubbles
There is value in a medium of exchange if users agree upon those terms. HODLing isn't that.
To the extent that the medium of exchange is valued, it is because it would be more convenient, less costly, less regulated or otherwise useful. BTC's mining, fees and slow transaction speeds subtract utility. Instead of moving onto better technologies, maximalists retreat to the illogical digital gold arguments. Ironically the inefficiencies are defended as creating value.
Also (as an aside irrelevant to my above question), I think you greatly overestimate the number of people who subscribe to a labour theory of value. Personally, I don't recall encountering people who subscribed to it other than far-left shitposters on twitter (who are definitely a minority, although a rather vocal one).
You don't need to look far to find posters using this argument to rationalize the value of BTC. Many contend that BTC's proof of work is the only possibility for a truely secure ledger, that the masses of computing power invested create the value of BTC.