It is not front running. These HFT are called market makers. Essentially, brokers show you the NBBO - National Best Bid and Offer. When you place an order on that price, one of the many market makers will pick it up. At any given point of time they will hold multiple buys/sells. So, they make money by collecting the spreads.

Nearly all brokers tend to sell order information to one or many market makers. It is neither illegal nor harm retail customers, not unless these customers are trying to run some HFT algos on their own.

This is highly illegal and taken very seriously. Is this speculation on your part or do you know this for a fact (in which case, you should report it).

It's been widely reported [0]. And as I said I feel like it's still a fair deal. Some HFT's get my orders and they know I purchased 2 AMZN yesterday a few seconds before it executed. In return I get to trade for free on their platform.

[0] https://www.bloomberg.com/news/articles/2018-10-15/robinhood...

Are you sure it's illegal in all cases? I was under the impression this was standard practice. https://www.cnbc.com/2014/03/30/michael-lewis-flash-boys-and...