Why couldn't MAX_BLOCK_SIZE be self-adjusting?
It certainly could be. The point of the post wasn't to arrogantly state what we must do or even that we must do something now. I would point out that planning a hard fork is no trivial manner so the discussion needs to start now even if the final switch to new block version won't actually occur for 9-12 months. The point was just to show that a
permanent 1MB cap is simply a non-starter. It allows roughly 1 million direct users to make less than 1 transaction per month. That isn't a backbone it is a technological dead end.
For the record I disagree with Gavin on if Bitcoin can (or even should) scale to VISA levels. It is not optimal that someone in Africa needs transaction data on the daily coffee habit of a guy in San Francisco they will never meet. I do believe that Bitcoin can be used as a core backbone to link a variety of other more specialized (maybe even localized) systems via the use of sidechains and other technologies. The point of the post was that whatever the future of Bitcoin ends up being it won't happen with a permanent 1 MB cap.
There are always altcoins to pay for the coffees, but still there can be no doubt that 1MB is not enough. I cannot believe people seriously oppose the increase! After all it will not make the blockchain 20x bigger, it will only make the blockchain as large as needed to include all transactions, once the 1MB limit is not sufficient anymore.
So people who oppose the change are basically saying, BTC transactions have to be severely limited (at around 7 TPS) forever, just to stick to the 1MB limit forever. That is nuts.