let's assume you are right. Also assume that the two people in the dark room are both somewhat rational investors. Then let's imagine that they are trading at a price that is significantly different than the open price. Why are they both OK with that price? If the price is higher, the buyer could be buying for less in public. If it's lower, the seller is the one that could sell in public for a profit. So one of the two sides is making an obviously bad decision.
The idea instead is that in a dark room, you can trade large amounts of shares without HFT interference. They'll probably be trading pretty much at the public price, just without sending all kinds of information about the fact that they traded into the world.
If I am not mistaken, the trade still has to be reported after the fact. What they are avoiding is leaking signals about what they want to trade before the trade occurs.
Let's assume you are right. If two parties trade a large amount of shares at the public price, how is HFT going to interfere if the trade took place in public?
1) Dark pools are not as secretive as folks in this thread think they are.
2) Those trades are happening at the public price. Its not too often that the dark pool trades will happen outside of the NBBO and usually those exclusions happen for very large block trades.
3) Most (all?) pools are reporting to FINRA by closing some may even report sooner after the trade.
So I am not sure what your question is as the data is fairly public already.
The idea instead is that in a dark room, you can trade large amounts of shares without HFT interference. They'll probably be trading pretty much at the public price, just without sending all kinds of information about the fact that they traded into the world.