EDIT: The rules also dictate the allowed prices the dark pools trade at. They have to be within the national BBO, they can't just trade at whatever price they want. So the public auction is actually helping them find the prices, without their pre-trade information affecting the price before execution.
I can easily see the retail price of a good, I can go to a wholesaler or some other holder of this good and ask them if I can buy it at a cheaper price. They might tell me to kick rocks if I don't have volume. Pretty similar to a dark pool. Markets are both private and public everywhere.
So if I have a RTX 4090 to sell (a very sought after commodity these days), and I sell it to my buddy rather than listing it on ebay, I'm doing market "manipulation"?
Same as "10 per store" limits when PS5s or whatever are in short supply, but then the CEO calls up the warehouse to get one for every student in their kid's class.