The fallacy is that a majority by any measure of voting has authority to dictate to the minority what the rules should be.
The fallacy is that anybody is forced to use BitCoin (in any form it is and might be), or that having a single person (in this particular case the developer of the BitCoin client) decide what the maximum money supply is, is better than the majority of the peers.
What Babylon said triggered some other idea directly related to the money supply. I've made another
thread.