HFT has reduced spreads of some equities to a penny, all market participants benefit from increased liquidity. Also, Citadel is buying retail order flow becaus

HFT has reduced spreads of some equities to a penny, all market participants benefit from increased liquidity. Also, Citadel is buying retail order flow because they’re reasonably certain they can capture the spread and not get run over by an institutional trader with more information than the market maker. They aren’t frontrunning your 20 share order because you aren’t going to move the market by purchasing 20 shares. Zero commissions and tight bid/ask spreads are better for an individual than no PFOF and $5/trade transaction fees with 25-50 bps bid/ask spreads.