Proof. Suppose that bitcoin has 1 million full nodes, and only one miner, that has 99% of the hash rate (say, the Chinese government) even though we believe that there are 20 different mining pools. Tell me what happens if the full nodes decide to implement, say, segwit, and the Chinese government switches to 20 MB blocks.
I'm no expert but I think what happens is you get a fork where all the hashpower goes to the 20MB block fork but those dumb bastards can't sell their coins because all the exchanges are broken.
The price plummets for months until someone can turn on a Radeon 5830 to mine on the segwit side until the difficulty drops after weeks or months. Segwit gets activated and we can all buy used chinese mining hardware at a super discount on ebay.
#UASF