Whoever you use to place stock market orders is also getting paid the same way. People have a funny idea of what a retail brokerage does. They do not execute orders on exchanges for you; that's a specialized capability that long ago became its own kind of company. Retail brokerages specialize in picking up the phone when you call with a complaint or request, and in advertising to acquire users.
You shouldn't care. The reason your order flow is valuable isn't that Citadel is trying to screw you. Rather, they can (occasionally) quote you better prices than they do the market as a whole, because they know you're not a giant investment bank or hedge fund about to roll over them like a freight train with a giant block order that will demolish every level of the order book. Internalizers can essentially arbitrage the difference. They're required by law to meet or improve the NBBO.