I'm very much in favour of raising the blocksize limit but this is just wrong, or it misses a crucial bit of information:

"If a majority of bitcoin miners “vote” for a particular upgrade then by definition this is the new version of bitcoin."

If their vote does not represent the economic majority then miners would only be creating unsellable blocks (for as long as they stay on the wrong fork). This is the hostile takeover by miners which Theymos and friends are so afraid of.

Still weird to be afraid of such an impossible thing. But important to understand their fears.

Because in reality miners would never go against the economic majority, they follow and they do not lead. So miners can vote for a hard fork but only if the economic majority indicated they are ready. Then the miners vote becomes a representative vote. Or maybe we should see the miners vote as only a vote for activation (as gatekeepers).

So company's like Coinbase are essential in paving the way for bigger blocks.