Spreads may have tightened, but payments for order flow suggest to me there's a new flavor of front running involved via HFT and dark pools. But I'm no expert.
How? No offence but it just sounds like conspiratorial nonsense based on some scary sounding terms.
Payment for order flow is an example of the incentives of retail traders, retail brokers and HFT market makers aligning. The market makers are able (and obligated) to improve prices because they have paid to receive flow they are almost certain is not toxic. Meanwhile they charge the likes of hedge funds higher prices as they can't guarantee the reasoning behind their trades (i.e. they may be about to have their faces ripped off).
The HFT firm takes their (tightened) fee for making a market, kicks some back to the retail broker, and because the broker earns money that way, they offer commission-free trading to the retail trader.
The book Flash Boys deals with this. It's a long time since I read it, but IIRC brokers need to split large orders and route them to different exchanges to get the best price (which is required under 'best-effort execution'). These orders will hit the exchanges at different times giving enough time for HFT to observe them at one exchange and front-run them at the other.
Are you worried about getting front run for fractions of a cent? I’m not. I’d rather have penny wide spreads instead of 1/8 dollar (or larger) like the old minimum tick size.
Dark pools reduce volatility, it’s just liquidity outside of the normal order book. Regular people don’t need dark pools because they aren’t slinging $500M block trades. Furthermore, trades can happen off-exchange without dark pools.
It sounds like you aren’t even an amateur, let alone an expert, no offense.
Payment for order flow is an example of the incentives of retail traders, retail brokers and HFT market makers aligning. The market makers are able (and obligated) to improve prices because they have paid to receive flow they are almost certain is not toxic. Meanwhile they charge the likes of hedge funds higher prices as they can't guarantee the reasoning behind their trades (i.e. they may be about to have their faces ripped off).
The HFT firm takes their (tightened) fee for making a market, kicks some back to the retail broker, and because the broker earns money that way, they offer commission-free trading to the retail trader.