you can do so at almost no cost. You only need 51% of the total hashrate, which is in turn maybe 10% of the total sha256 mining power, so you need 5% of that. What's worse,
if you start mining BCH after it becomes marginally more unprofitable, because you're also compensated by a bribe or by an ideological payoff, rational honest BCH
miners will switch over to BTC, leaving only the attackers mining BCH.
