Many exchanges have limits on the number of order cancellations you can make. You get penalized if you send too many cancels compared to the number of trades you get.
Besides, most retail orders go through brokers, not directly to the exchange, and the brokers can provide their own layer of algorithmic sophistication to help the clients get a better price than if they were to place the orders on the exchange on their own directly. This can be done by internally matching orders on both sides, as well as placing orders at strategic times and prices, also using algorithms.
So, this isn't really about "poor retail investor" against "evil predatory high-frequency trader".
Besides, most retail orders go through brokers, not directly to the exchange, and the brokers can provide their own layer of algorithmic sophistication to help the clients get a better price than if they were to place the orders on the exchange on their own directly. This can be done by internally matching orders on both sides, as well as placing orders at strategic times and prices, also using algorithms.
So, this isn't really about "poor retail investor" against "evil predatory high-frequency trader".