Sometimes identical products trade at different venues, often different products at different venues are highly correlated. HFTs reduce the friction of value transfer between these many different markets. They are, in a sense, building the neurons that make up the global economic central nervous system. It's a natural and healthy market phenomenon. The benefits are systemic, which requires some perspective to appreciate. In the course of a decade or two, HFT has permanently cemented itself into the fabric of the finance.
All this talk about front running is uninformed utter nonsense.
All this talk about front running is uninformed utter nonsense.