Can you tell me more about these commitments and what makes them expensive? No one may explicitly choose to trade with HFT firms, but that doesn't mean they do

Can you tell me more about these commitments and what makes them expensive? No one may explicitly choose to trade with HFT firms, but that doesn't mean they don't value their presence "Although Vanguard does not engage in "high frequency trading" and does not operate a "dark pool," we believe much of the public concern over "high frequency trading" is misplaced and believes such activity, appropriately examined, contributes to a more efficient market that benefits all investors." http://www.sec.gov/comments/s7-02-10/s70210-122.pdf http://www.sec.gov/comments/s7-02-10/s70210-122.pdf