It's clear that there is confusion between toxic HFT activity like spoofing, and liquidity providing/arbitrage. The later provides a great service to market quality and price discovery.
I'm not so sure its possible to draw a such a line, HFT likes to make itself out to be the great saviour doing everyone a favour, but at its heart, HFT only makes its money one way ... spoofing, queue-jumping and other toxic activity.
Afterall, if HFT were only "doing good" and providing liquidity then they would not need to spend millions on specialist fibre and radio links etc. etc. would they !
