Here's an interesting proposal - you charge a small amount (e.g. 0.001 of a cent) for every single order placement and rebate the proceeds to all market participants in proportion to how much volume they actually traded.
People who enter many quotes that they never trade on would be punished by this system (human traders and "flickering" high frequency traders alike) whereas people providing genuine liquidity, in the form of long-lasting quotes at a good price that they intend to trade, will benefit.
People who enter many quotes that they never trade on would be punished by this system (human traders and "flickering" high frequency traders alike) whereas people providing genuine liquidity, in the form of long-lasting quotes at a good price that they intend to trade, will benefit.