Why is HFT not allowed?

Why is High-Frequency Trading (HFT) not allowed in certain financial markets? Could it be due to concerns about market manipulation, unfair advantages for those with faster technology, or disruptions to the overall stability of the market? How does HFT impact retail investors who may not have access to the same resources as large institutional traders? Is there a balance that can be struck between allowing for technological advancements and protecting investors from potential harm?