HFT costs 'everyone' that uses the stock market though an intermediary money so it really does cause income inequality. To suggest otherwise is to suggest they can somehow increase the value of stocks on average when they don't increase dividends and profit from the stock market. AKA money magically appears from nothing without costing anyone anything.

Which is not to say every single person is worse off just that this does not increase the long term value created by the companies who's profit makes the stock market a positive sum game.