This is usually pushed by someone with an opposing view (who strangely enough didn't have the conviction to bet the other way) and is just a roundabout way of them patting themselves on the back for finally realizing what he could see so clearly from beginning (and still hasn't make money on the reversal).
Something happened to push this hard. We might not know what it is for a generation, but there is a logical reason. Constantly reducing a supply to allow pressure from the value it gets from demand makes it highly volatile (prices are intersection of the value of the currency and value of the item - and BTC's deflationary stance basically starts adding 0s to the front of the price 0.1 goes to 0.01 and now currency and demand swings are 10x greater). constant large swings make it a shitty currency - so over time is will fail.
Now, if only these other cryptofxs can get their shit together and shot with the constantly deflating things - yes it make the knownothings come running for a piece, but overall it will fail.
Please no Keynes quotes about irrationality. It is something he pulled out of his ass that isn't provable or disprovable. It makes a great soundbite and a terrible argument.