[rswail]

The systemic risk is because the intermediaries have to use their liquidity to keep the system moving, not because the short sellers might go bankrupt.

Trading in securities with daily settlement, while movement of money is not operating on the same frequency, means that there is a requirement for someone to take that risk.

That's the systemic risk, not the trading itself. If the execution, settlement, and clearing of a trade were simultaneous and instantaneous, then there's no risk to the market itself.