Clearing trades

The DoJ is pushing for a seperation of trading and clearing. The FT explains why this is important.
FT.com Futures reform:

"When an exchange controls clearing, it can prevent a customer from buying a contract on one exchange and selling it on another. Customers, therefore, have everything to gain from the DoJ’s move. The US stock markets, where exchanges share a common clearer, are undergoing fierce competition that has seen tariffs slashed, spreads tightened and volumes soar."