ACR MLG DSNDED BELOW GS ON STADIUM VISUAL AT LAX IN RESPONSE TO TCASII RA.

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ON DOWNWIND FROM SMO WE WERE ASKED TO TURN BASE LEG IN THE AREA OF THE COLISEUM. HAVING THE ARPT IN SIGHT AND THE PRECEDING AIRPLANE ON SHORT FINAL (FOR 24R); WE WERE GIVEN A VISUAL APCH (ALSO FOR 24). ON ABOUT A 2 MI FINAL WE WERE ISSUED TFC AT 2 O'CLOCK; AND WERE TOLD THAT IT WOULD PASS OVER AND BEHIND FOR 24L. BTWN 1000 FT AND 500 FT WE RECEIVED A TCASII RA ALONG WITH THE AURAL WARNINGS. TFC WAS NOTED TO THE R AND SLIGHTLY BEHIND; WE IMMEDIATELY INCREASED OUR DSCNT ACCORDING TO THE RED AVOIDANCE AREA; THEN OF COURSE WE RECEIVED THE 'MONITOR VERT SPD' AND 'BELOW GS' WARNINGS! APPROX 20 SECONDS LATER I OBSERVED A COMMUTER ACFT WINGTIP TO WINGTIP FOR 24L. AS OUR AIRSPD WAS SOMEWHERE AROUND 140 KTS; I WONDER HOW HE COULD COME OVER THE TOP OF US AND CATCH UP SO AS TO BE ABEAM FROM A DOWNWIND LEG! I FEEL THE PRACTICE OF XING ACFT; WHERE ONLY 1 ACFT HAS VISUAL CONTACT WITH THE OTHER ACFT; IS DANGEROUS. UNDER THE CIRCUMSTANCES; WE SHOULD HAVE BEEN GIVEN THE L RWY AND THE COMMUTER THE R. ALSO MUTUAL VISUAL CONTACT SHOULD BE MAINTAINED BY BOTH PLTS AT ALL TIMES. (THE RWYS ARE ONLY 800 FT APART.) INSTANCES SUCH AS THIS ARE PARTICULARLY UNNERVING; ESPECIALLY IN A TCASII ENVIRONMENT. THIS ADDS ADDITIONAL CONFUSION WITH LOUD AURAL WARNINGS AT A TIME WHEN THE WORKLOAD IS AT ITS HIGHEST. I WOULD LIKE TO SEE GREATER SEPARATION FOR ARRIVING ACFT. AS A FURTHER SUGGESTION; FOR SAFETY; THE COMMUTER SHOULD HAVE BEEN TOLD TO REMAIN AT LEAST 1 MI BEHIND.