HFT could easily be a form of arbitrage. If we understand a wide bid-ask spread and/or a market slow to react to a large order as being essentially a rent for

HFT could easily be a form of arbitrage. If we understand a wide bid-ask spread and/or a market slow to react to a large order as being essentially a rent for the large trader, then HFT narrowing the bid-ask spread and allowing the market to react more quickly to the large order takes that rent and divides a fraction of it to the HFT and another fraction of it to whoever is ultimately trading against the large trader. So instead of this rent (amount of money X) getting all captured by a single player who is necessarily a large, wealthy trader, it gets divided up more broadly. That sounds like a textbook case of arbitrage being in the public good. HFT does that. Does it also do other things which create rents rather than break them up? Hard for me to say. It's a complicated subject.