If this proposal has less than half of the total hashpower (or is it even less than 75%? Haven't quite thought it through completely) supporting it, I can see the following happening if the sum of supporters and people who want to screw the supporters out of money is at least 75%:
Non-supporters create blocks with the new version, but don't actually implement the rule. Then after the new rule is locked in, miners will create too-large blocks that are rejected by the majority. If the percentage is less than half, then from their perspective, they will essentially be on the losing  side of a soft fork, and they'll be losing money by mining for nothing, even from their perspective and that of e.g. users and merchants who have upgraded. 

On Saturday, August 15, 2015, Milly Bitcoin via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:
So if you want a user vote, that's an issue that'd have to be tackled:
the people who admin the main communication channels Bitcoin users have
vowed to censor any program that doesn't slavishly follow 51%+ hash
power. That attempt to control the conversation is certainly not
libertarian or democratic in nature, but there you go.

These types of actions are immediately apparent to anyone who looks at the Bitcoin ecosystem (Bitcoin.org, Githib, Wiki, bitcointalk, etc.) and were readily apparent long before any block size debate.  It is almost a taboo subject and anyone who raises these types of issues is immediately labeled as a "troll."  These are the people who used to run around saying that Bitcoin development is "decentralized" because anyone can fork the code and now many of the same people claim a fork will destroy everything.

The problem is that a small group of highly irrational and inexperienced people (outside of the small and unusual Bitcoin ecosystem) have control over the majority of the resources.  I think over time the problem will even itself out but currently it is an obstacle in moving Bitcoin forward.

Russ


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