But wouldn't the long-term honest mining be more profitable than a single hit and run? Kinda the same reason that when you go to a restaurant the restaurant owners almost always exchange food for money rather than rob you and leave town forever. If you own a restaurant it's generally more profitable to run it honestly than run away with a one-time dishonest payoff.
Not if it destroys the credibility of a rival coin, which I suspect could be the case here. Many in the "real Bitcoin" community call Bitcoin Cash a fraud because its existence reveals the specious value of their "real" cryptocurrency.
Executing a double spend attack on Bitcoin Cash would be a massive success for Bitcoin owners. Same goes for Bitcoin Gold.
You could even create a mining pool/network - let's call it CoinFucker - where every now and then the pool's resources were diverted to attack a rival coin. Doing so damages that coin's reputation, and in doing so reduces the competition. This would be a great way for the majority of mining/computational power to squash would-be rivals.
I'm not sure in this specific case it would make sense for Bitcoin users. Unless you are already involved in cryptocurrencies, I'm not sure the average person is going to differentiate between "Bitcoin" and "Bitcoin Gold" -- the negative impression of "Bitcoin Gold hit by attack" is going to reflect on the original Bitcoin.
Depends on if you feel that the crypto would continue to have value in the long term. If you've amassed that much power (or are close to it), and you didn't feel the coin was going to hold value long term, why not?
