You're right that the article doesn't address that counter-argument, but the suggested means of profiting from the attack is immune from it:

> A successful 51% attack, indeed even a credible threat of such an attack succeeding, would almost certainly sow fear and uncertainty in a wide range of public markets. An attacker could leverage this because they would have a certain amount of control over when news of the attack broke, so they could (for example) take a short position on a portfolio of financial stocks before launching the attack.