Brokerages have a duty to their traders. I imprecisely spoke when I used fiduciary as recent guidance says they have the lower “suitability standard”. With regard to fills they are covered by reg nms and the nbbo. All of that is a much stronger regime than Facebook is under and to my opinion Facebook uses their power much more detrimentally. Reasonable people can disagree on that.

All retail brokers besides vanguard and IB’s paid tier sell order flow. This enables cheap/free trades and low spreads which I view as well worth the execution difference ymmv.

I’d also suggest if your mental model is that citadel is doing risk free front running you don’t understand market dynamics correctly.

In any case it’s cheaper for me to execute my retail trades than any time in history. I’m good with that outcome.