I do have a half-written tech report detailing how a cartel of miners could force a change in the rules; but that has become common (if still denied) knowledge by now, so it would probably be rejected for that (if not for ideologocal reasons).
So let's say a majority of miners change the rules in a way that the rest of the bitcoin community does not agree with, then what?
What prevents the core developers from just changing the hash function, rendering all mining hardware useless and let the whole mining business start from scratch? Yeah it would be pretty messy, but the mere existence of that option keeps the miners in check.
That is the conventional argument that is used to dismiss that problem. It is like the Captain "defeating" a sailor''s mutiny by taking off in a small lifeboat and declaring it to be "the real ship"...
The Core developers would have to convince all bitcoin users to get into that small boat with them and discard the coins that they have on the carte's branch of the chain. Good luck on that...