It adds liquidity and that does more good than bad for everyone, whether you’re a retail investor looking to enter or exit a position without facing a hefty ‘tax’ from a wide bid-ask spread, or you’re managing an ETF and need to dump 300k shares of something while rebalancing.
Without HFT a lot of tickers would look like options and futures contracts - no volume, wide spreads, and rife with abuse from people walking orders up and down