Why is HFT controversial?

Why has High-Frequency Trading, or HFT, become such a controversial topic in the world of finance? Some argue that it offers significant benefits to the market, such as increased liquidity and efficiency. However, critics contend that HFT gives an unfair advantage to those with the fastest computers and access to complex algorithms, leading to an unequal playing field. Furthermore, they claim that HFT can contribute to market volatility and even flash crashes, where prices plummet suddenly and then rebound just as quickly. So, what are the real pros and cons of HFT, and how should policymakers address these concerns?