But human market makers colluded routinely, and in some cases famously.
My only point was that some people think all HFT is bad, and here we have a complaint that actually the situation is reversed and it was actually all human market making that was bad. I don't think either statement is completely true, and I was trying to highlight the contradiction because the human market makers and the HFTs are, in a lot of cases, the same people.
† https://www.bloomberg.com/view/articles/2013-11-06/cftc-sues...
I think it's harder to describe how HFT is bad. Most of the efforts in this thread are, we'll say, only loosely connected to reality.
The best you can say about sweaty men shouting is that if not corrupt, still inefficient. (To say nothing of spreads in eighths.) I think that's a claim that really is true for literally every trader.
You also could see who was on the other side of your trade. Savvy floor traders would use that information to their advantage. If a sharp broker traded with you, you could hedge more aggressively or speculate in the same direction. Most electronic markets are anonymous these days so there's less information leakage.