[harryh]

I thought HFTers only got involved in between two parties when they knew they could make a profit.

You thought wrong. While there are a variety of things that HFT firms do, most of it is market making.

https://en.wikipedia.org/wiki/Market_maker

[HWR_14]

Those market makers are known, formal and regulated. HFTs are none of those.

Well, I guess semi-regulated.

[harryh]

The big HFT firms are, in fact, well known.

https://medium.com/automation-generation/15-well-known-high-...

They're also regulated in various ways.

[kasey_junk]

In fact all of the nyse designated market makers are HFT firms.

https://www.nyse.com/markets/nyse/membership