HFT is about faster price discovery and often is just arbitrage between exchanges.
If the New York Stock Exchange price of AAPL is $1 more than the Chicago Exchange, then a HFT detects that and buys the Chicago Exchange’s AAPL + sells NYSE AAPL, bringing price discovery to the masses.
That’s why HFT is, in practice, allowed. Because the vast, vast, vast majority of HFT is important arbitrage between our collection of exchanges in the USA.
These “dumb” price differences need to be fixed, and it makes sense for the people who discover these differences to profit from them. It also provably makes the markets smoother and better for everyone involved. (New York can know that the price changes over in Chicago will affect them within milliseconds, keeping all the exchanges across the country nearly in sync).