"Modern criticism of high frequency trading is a continuation of a long tradition of distinguishing the activities of Monied Men investing in the market and Traders speculating within the market. As such it can get entangled in a web of social judgements, such as it is OK for the rich to gamble but not the poor. To make decisions about HFT, therefore, requires some understanding of this mess."
This is the same issue that arises time after time through Thomas Mortimer, Keynes and into the assessment of HFT. The role of speculation in the market is a major issue. One interesting point that Tim makes is that Big Bang blurred the line between broking and speculation.