I don't get it. The article first criticizes HFT for making markets rather than speculating, incorrectly asserting that it's somehow a tax on traders (hint: don't cross the spread if you don't want to pay the "tax"). Then it reveals that HFT does speculate - they pay people to do market research and trade on that basis, which is somehow also evil.
Damned if they do, damned if they don't I guess.
The authors reasoning in going from HFT engaging in speculation to a financial transaction tax is unclear. He wants to prevent speculation and information gathering? Or prevent people from speculating quickly?