Its more like 50% of total volume being traded in dark pools. Your price argument does not make much sense though, the beauty of western markets is that folks are so opportunistic that someone will exploit any information asymmetry so your argument would not hold up. Also at the end of the day its not like buyers and sellers in a dark pool know "the price" of what they are trading, sure they have ideas of where they might be buyers and sellers but they are still using the lit market data to inform their decision.