I don't think it's illegal to tell others your stock bets. He discovered a vulnerability in the over leveraged short positions of GameStop stock and made the case public. Why should it be illegal? I am sure he used and acted on available public information.
Why would long term investors and society as a whole care about high frequency traders? They pay their fair share of taxes to society as anybody else. No high frequency traders, less govt income. So you want to exempt yourself but get rid of institutional traders?
$30*300*0.001*10 = $90 a day, $90*250 = $22,500 annually if one side is taxed.
$180 a day, $45,000 annually if both sides of a transaction are taxed.
Against available trading capital of $30 * 300 = $9,000.
What is the difference between professional traders and retail traders exactly in terms of tax impact? Are you saying that unlike retail traders professional traders are holding their positions long term?
If the cost is 'negligible' then what is the point of having the tax? One can't have it both ways, create a revenue stream out of taxing people and claim that the tax cost is small. Small cost leads to a small revenue.