The Bitcoin Wiki states "A profit-seeking person will always gain more by just following the rules, and even someone trying to destroy the system will probably find other attacks more attractive."
I'm always (!) wary when people claim "always" or "never". Similarly I challenge the above statement, that seems quicker to try to reassure than to really analyze the validity of "always" in the context of being a good/bad actor.
What about the situation whereby some entity builds up a hugely leveraged short BTC position. e.g. say two nations took a HUGE bet each on opposite sides of the bitcoin price. Then the nation on the short side could secretly collude with a 51% miner to destroy the network and profit from the resulting BTC crash, kicking back to the miner a slice of the winnings.