Light bulb: tax all tradings with a tax percent increasing with the number of transactions per second, in a continuous way (even for less than 1 t/s) that would not make any difference for regular traders (and have a tweakable taxing formula that could regulate a market's stability and sensitivity to information by letting more or less HFT happen by setting the 100% taxation limit - the HFTs will have all incentives to stop trading when they are taxed 100% or beyond - i.e. when they are "fined")!
