A B757 FLC RECEIVED A TCASII RA FROM A HVY JET WHILE MAINTAINING VISUAL SEPARATION NEAR LAX.

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CLRED INBOUND ON MITTS STAR TO N COMPLEX AT LAX. SOCAL APCH ASKED US THAT WE HAD A HVY JET THAT WOULD JOIN THE CIVET ARR TO THE S COMPLEX. WE RPTED IT IN SIGHT AND WE WERE TOLD TO MAINTAIN VISUAL SEPARATION AND GIVEN A LOWER ALT ALONG THE STAR. WE PASSED BY THE HVY JET WHICH WAS TURNING FROM A BASE LEG TO JOIN THE STAR AND SHORTLY THEREAFTER; WE RECEIVED A TCASII RA FOR THE HVY JET WHICH WAS AT OUR 8 O'CLOCK POS; HIGH AND DSNDING. IT WAS IMPOSSIBLE TO JUDGE THE RANGE TO THE HVY VISUALLY (TCASII SHOWED IT TO BE LESS THAN 1 MI). WE COMPLIED WITH THE RA BY DSNDING BELOW THE PRESCRIBED ALT PROFILE ON THE STAR. WE ADVISED SOCAL APCH THAT WE HAD COMPLIED WITH THE RA. THE RESPONSE WAS A DISINTERESTED 'YOU HAVE HIM IN SIGHT; DON'T YOU?' AN OVERSHOOT OF THE CIVET STAR BY THE OTHER ACFT MAY HAVE OCCURRED LEADING TO THE TCASII RA. VISUAL SEPARATION AT NIGHT IS UNSAFE. BUT WOE BE TO THE PLT WHO DOES NOT ACCEPT IT GOING INTO LAX. THE CTLRS WILL DENY LOWER ALTS AND APCH CLRNCS TO AN ACFT NOT WISHING TO ACCEPT VISUAL SEPARATION.