* Finally, one of them claimed that, if the cartel decided to do that, the, rather than accept a small compatible change to the protocol, surely all users would make a big incompatible change to the protocol, alienate all the miners, and go back to the network of 2010. And closed the discussion with "QED".
That was not the argument that proved your scenario unworkable. Maybe we need three of four posts before you read it, rather than throwing up a straw man and ignoring that your scenario fails.
We were down to discussing the "Red Button" solution. Wasn't that your argument?
Also the change you claim (incorrectly) users would accept is not a "small compatible change," it requires users to accept a hard fork. That's not compatible and its not small. Its perhaps the only thing that would indeed make another hard fork clearly (as) viable -- since users would simply be choosing between one hard fork or another.
Whether the users would accept it or not is a matter of belief, and clearly we have vastly different views about the mindset of the bitcoin community. What we can discuss objectively is what are their choices and the respective gains/losses.
Yes, either change in the protocol would require everybody to upgrade their client software, and recompile private software with upgraded libraries and/or parameters. Like other hard forks in the past, and hard forks that will surely be necessary in the future, cartel or no cartel. But the Red Button fork is way more radical than the cartel's.
Moreover, after the cartel's fork, only one branch will be viable, so most users will upgrade to it, and the price may not suffer; whereas the Red Button fork will result in two functioning "bitcoins", so the price will be split among them.
