The max block size is not imposed by fiat, but by agreement to a convention. You could change that in your client right now and produce blocks just fine, but unless at least 50% of generators agree with you, whenever your client produces a block that defies this agreed convention it will be ignored by those who do.
By fiat, I don't mean to suggest that someone dictated it with an iron fist. But I do mean to point out that it makes the currency dependent on a central authority.
No, its not dependent on a central authority. And fiat means imposed using force or thread of force. Please dont change the meaning of the definitions because it makes discussing things harder and tedious.
Sure, it is open source, but it is meant to benefit humankind, not just developers... over 99.9% of its users will have no clue how to participate in the management of this convention, which at this point appears to be designed to require it.
No. If someone wants to change it, you just need one developer changing the source and making it available in the Internet. Things are always going to be like this, people have different knowledge. The developers are not a unit, they are different people that can take different decisions. The software is open source. A group of people could even pay a developer to implement the changes they want. Anyone can make what they want with bitcoin. Bitcoin works by voluntary agreement.
Wouldn't it make sense to change the convention to something that will automatically cope with growth
I dont understand what you mean by "cope with growth" (growth of currency, growth of prices, growth of GDP, economic growth, ...?).
That said you wont be able to make a software that is 100% versatile for any change you can imagine. A software is always limited and actually its bad if you try to make it too versatile. My experience shows that it is better to keep a software simple and that solves a practical task, not some range of remote posibilities.
, much like the difficulty system adjusts to new computational pressure? With a hard limit like this, the threshold at which it suddenly grinds reliable transaction processing to a halt at a reasonable price (until everyone upgrades their client at the direction of the developers) will, in all likelihood, be exactly at the moment where it sees a viral surge in new popularity that suddenly brings it past that point and to its knees. That may bring it a lot of unnecessary questioning and criticism by the public and the media, particularly about just how truly viable and independent it is.
I have read repeatedly that the achilles heal of Bitcoin is that 50% CPU threshold. I have never heard of another one I believe might exist - the possibility that the Bitcoin community gets very large, and then has factions, the block chain forks, and the system crumbles in the face of FUD while two or more camps argue which leg is correct (sort of like a country that started out with a Constitution or a religion that started out with a Bible or Koran and now has two large factions eternally asserting their particular interpretation of it). Two religious factions can go their own way and live their own separate lives on separate lands, but if they must trade while they can't agree on what constitutes the existence of money, the money may as well not exist. If Bitcoin is in its "constitution" phase, I would submit that the time to address something like this is now.
Competing currencies is very common and it does not have to undermine bitcoin. If bitcoin forks it will just strengthen the system. There will be exchange places where you will be able to buy or sell one bitcon currency for another if you need to, etc... In fact, I have said since the beginning that the its inevitable that different bitcoin chains appear. I think the division will be by physical territory, but who knows really.