That's true, he is making a black-and-white argument, where I am making a more probabalistic or practical argument.  The agreement system of checkpointing is a working agreement system, it just has different practical characteristics than Bitcoin so I don't consider it as a possible stand-alone protocol.  It lacks the strength of the original.

Also I see what you're saying about the developers.  They could either displease the majority of users, resulting in a permanent fork, or a schism could arise among the developers themselves, also resulting in a permanent fork, although they would have to be convincing to drag a significant number of users with them.  So far this has not happened.  In all of the forks in the open source world, I don't personally recall any that actually destroyed their project.

This reminds me of some new features introduced into Gnome/Ubuntu, that a loud minority of users rejected, or else the split of OpenOffice into LibreOffice.  While somewhat damaging, the community did survive.