FLC OF DC9 BREAKS OFF CIRCLING APCH DUE TO PROX OF TFC THEY ARE FOLLOWING. GIVEN #3 FOR THE APCH BUT NEVER INFORMED OF POS OF OTHER ACFT ALSO CIRCLING.

Narrative

FLYING THE RWY 31C APCH (ILS) AT MIDWAY CIRCLE TO LAND RWY 22L; AT NIGHT. STARTED TO CIRCLE; TWR CLRED US TO LAND RWY 22L '#3' ON APCH. TWR NEVER STATED WHERE THE OTHER ACFT WERE. WE CONTINUED TO MANEUVER SE OF FIELD AND WERE SETTING UP FOR A 3 MI FINAL. ON DOGLEG ANOTHER ACFT RPTED THAT WE WERE GOING TO CONFLICT WITH THEM ON FINAL. TWR THEN TOLD US TO TURN SLIGHTLY R AND POINTED OUT OUR TFC AND WE SAW THE TFC -- TRIED TO MANEUVER BEHIND THEM AND CONTINUE THE APCH; BUT WAS STILL TOO CLOSE SO WE BROKE OFF THE APCH. BEING AT NIGHT; WITH TOO MANY ACFT IN THE AREA CREATED A POTENTIAL DANGEROUS SIT. UNLESS YOU CONSISTENTLY DO THIS APCH; THE WORKLOAD ON 2 CREW MEMBERS IS TREMENDOUS. THIS ARPT ALONG WITH THIS APCH IS AN ACCIDENT WAITING TO HAPPEN. WITH THIS APCH; WHEN THE CIRCLE IS INITIATED THE FO COMPLETELY LOSES SIGHT OF ARPT. THEREFORE; THE FO MUST MONITOR THE CAPT FLYING; ANSWER RADIO CALLS; LOOK FOR THE RWY; LOOK FOR OTHER ACFT THAT HAS THE TCASII LOOKING LIKE A CHRISTMAS TREE AND DO THE CHKLIST. I KNOW THIS IS WHAT WE NORMALLY DO ON AN APCH BUT A CIRCLING APCH IS MUCH DIFFERENT; WHICH LEADS TO MY QUESTION OF WHY NOT JUST FLY THE RWY 31C APCH TO A LNDG; ESPECIALLY AT NIGHT. WITH ALL THE GND LIGHTS IT IS VERY EASY TO LOSE THE RWY AND/OR THE PRECEDING ACFT.