Agreed. The authors make this point in order to move on to the main analysis of the paper: The Goldfinger attack.
"As described above, a 51% cartel attack is unlikely to generate enough reward within the Bitcoin economy to be worthwhile to the attacker. However, this does not rule out the possibility of a 51% attack that aims to destroy the Bitcoin economy in order to achieve utility outside the Bitcoin economy. We call this the Gold nger attack after the character in lm who tries to undermine U.S. currency by ruining its gold backing [15].
There are at least three possible motivations for a Gold finger attack. First, a government or institution might want to block Bitcoin transactions, to enforce the law, deter money laundering, or achieve some other institutional goal. Second, a non-state attacker might seek to gain some political or social goal, perhaps as a form of social protest (such a model was previously postulated by
Becker et al. under the name \Occupy Bitcoin" [6]). Third, an attacker might seek an investment gain, for example by taking large short positions in Bitcoins so as to profi t if the value of Bitcoins is diminished. In all of these cases, the attacker must achieve enough utility to justify the
substantial cost of an attack. We agree with Becker et al. that it is unlikely that a protest movement could muster the resources to launch a successful attack. And at present it does not appear possible to acquire a short position on Bitcoins that is large enough to justify an attack."
One of the best papers published on the game theory of Bitcoin to date in my opinion.
"As described above, a 51% cartel attack is unlikely to generate enough reward within the Bitcoin economy to be worthwhile to the attacker. However, this does not rule out the possibility of a 51% attack that aims to destroy the Bitcoin economy in order to achieve utility outside the Bitcoin economy. We call this the Gold nger attack after the character in lm who tries to undermine U.S. currency by ruining its gold backing [15]. There are at least three possible motivations for a Gold finger attack. First, a government or institution might want to block Bitcoin transactions, to enforce the law, deter money laundering, or achieve some other institutional goal. Second, a non-state attacker might seek to gain some political or social goal, perhaps as a form of social protest (such a model was previously postulated by Becker et al. under the name \Occupy Bitcoin" [6]). Third, an attacker might seek an investment gain, for example by taking large short positions in Bitcoins so as to profi t if the value of Bitcoins is diminished. In all of these cases, the attacker must achieve enough utility to justify the substantial cost of an attack. We agree with Becker et al. that it is unlikely that a protest movement could muster the resources to launch a successful attack. And at present it does not appear possible to acquire a short position on Bitcoins that is large enough to justify an attack."
One of the best papers published on the game theory of Bitcoin to date in my opinion.
http://weis2013.econinfosec.org/papers/KrollDaveyFeltenWEIS2...