I don't really want to start a debate on how HFT produces real-world value, but just consider that if these things you talk about are really useful and valuable, they might also provide competitive salaries to attract people?
What pays the most only loosely correlates with what produces the most value for society. It's easy to skim a percent here and there off hundreds of billions in volume shuffling around without the owners of those billions caring much, but it's much more difficult to see how that, on the whole, actually improves the condition of your neighborhood.