[hsitz]

"Since when do we judge compensation based on value added to society, and if that's what we do, why don't we apply that approach beyond finance?"

We apply it in finance for a couple reasons. Securities exchanges are high regulated entities, at least since the Great Depression brought our country to its knees. Ever heard of the SEC, which exists to protect investors? There is no reason for HFT to be allowed at all unless it is creating a net benefit for society. Or said another way, if HFT provides a benefit only for the people doing HFT, and has a negative effect on others, then there's no reason to allow it. (An aside: My understanding is that studies have shown markets to have plenty of liquidity without HFT.)