Alright, it's hard for me to explain how sometimes all means all and sometimes it doesn't. But tptacek's comment didn't literally say that every last floor trader was crooked, just that was generally true. And it's easy to see how it could be true. A wink here, etc. The difficulty for anyone to see the size of the order book.

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.