But he can't stop federated pegged side chains.
And pegged side chains are superior risk management strategy versus an all-or-nothing risk of Bitcoin vs. altcoin fork war (from a diversification standpoint, i.e. you buy the altcoin if you want upside ROI but don't have to worry about being diversified against ELE or a radical transposition of wealth effect if you hold 100% in BTC). Less risk means more adoption of crypto-currency in general.
Note I think altcoins can coexist and benefit from pegged side chains (nullifying the risk that pegged side chains could copy and steal value from innovation, i.e. threat of Communism!). They just need to be clever about what they do once pegged side chains are a reality in the market.
P.S. they ought to just increase the block size slightly and incorporate the SPV now, but unfortunately the myopic politics is slow to catch up to reality. Any way it will all be subsumed as I described:
No worries. Core is doomed. A pegged side-chain with SPV built-in will win. Then minority Core will be 50+% attacked into oblivion. MPEX's short will be nullified by the peg.