Before we dismiss Dimon's arguments as motivated by a conflict of interest, or simple ignorance, doesn't it make sense to try to understand them? And to consider both the context of his remarks, and what recent history suggests (while remaining aware that history suggests - it neither dictates not even predicts).
First of all, a key point is that the intended audience is not people with some expertise in cryptocurrency but a general financial audience.... people seeing the huge spike up in prices who may be tempted - while ignorant - to rush in and buy bitcoin or ether or an ICO.
As an INVESTMENT there are reasonable arguments that Bitcoin will fail, and that best hopes & prospects have been disproven. Putting aside its role as one gateway into the world of cryptocurrency, the hope that it would become a viable, widely-used payment system for the general public is now a lot less plausible than it was just 3 years ago.
It's too slow, too expensive etc. The higher the price of a greater the volatility, the better the trading opportunities - and the worse for actual payment use, and thus for a long term role in real world payments.
Sure, no one can see the future. Bitcoin may survive... But is it really plausible to believe that the original invention will represent the final word - where the entire crypto world is deploying efforts, new tech innovations, learning from past failures successes & shortcomings, to improve on the original model?
The last time the collective wisdom learning & ingenuity of man was not able to improve on a new technology? Fire v1.0?
Bitcoin's contributions are many . . . but anyone can copy & improve on them.
How do you know if you're reading a worthwhile response to Dimon? Does it make a distinction between the blockchain - available for copying and improvement by all - and the overpriced semi-used payment tokens of the original bitcoin network? Does it discuss the early days of the Internet but without making the distinction between Internet-the-technology and early websites that were thought to be extremely valuable but have long since vanished?
Dimon's criticism is harsh - and will be wrong about many aspects of how the future plays out - but it points to considering whether there are some useful hints from history, at least as far as possible pitfalls to watch out for.