So, first off, I am not saying internalizers are all evil and that pfof is bad. That $2.40 your retail trade earned the internalizer is the price you pay for convenience and immediacy. You let someone else handle the order and they do what they want with it - within certain guidelines.

You could have saved the hypothetical $2.40 had you traded differently, albeit slower, and caused less market impact with your order. Of course, trading slower comes with its own slippage risk or opportunity cost that the market moves out of your favor. But it could also move in your favor... However, if you let a greedy HFT use your order to impact the market - it will always be out of your favor.

For a small retail guy, you are powerless unless there is a RobinHood 2.0 that decides to offer comm-free trades + does not sell your orders + makes money doing something else ... stock loan maybe?

EDIT: Also the HFTs hate limit orders because it reduces the amount they can internalize. They also generally have a contractual obligation to always execute your order. So you can always use a limit at or inside the offer if youre buying, and potentially save on that cost.