B767 CAPT DSNDS BELOW MSA OVER FO'S OBJECTION DURING VISUAL APCH TO OAK.

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THE CAPT WAS FLYING. WE WERE CLRED FOR A VISUAL APCH TO RWY 29. THE CAPT BRIEFED THE APCH TO USE ILS RWY 29 AS A BACKUP AND WHEN 21 MI S OF ARPT; DSNDED TO 2500 FT MSL TO 'INTERCEPT' THE ILS. I WAS TELLING HER THAT WE WERE STILL WELL S OF THE ARPT; I WAS CONCERNED THAT WE WERE TOO LOW OVER PEOPLE'S HOMES AT THE ALT AND WHEN WE CONTINUED PAST 3000 FT MSL APCH CTL WARNED US THAT WE HAD DSNDED BELOW THE MSA (FOR THAT AREA OF 3900 FT MSL; WHICH THE CAPT HAD BRIEFED). SHE BEGAN AN IMMEDIATE CLB TO 4000 FT MSL; THE APCH SAID 'YOU ARE NOW SAFE TO DSND AGAIN FOR THE VISUAL APCH.' THE CAPT HAD EARLIER TOLD ME NOT TO OVERREACT IF WE WERE NOT FLYING INTO A MOUNTAIN; AND THAT'S WHAT THE ASRS PROGRAM IS FOR.' I BELIEVE THAT COMPANY PROCS EXIST TO HELP THE CAPT. PF/PNF DUTIES; I BELIEVE; DO NOT TAKE AWAY FROM A CAPT TO COMMAND; RATHER; I BELIEVE THEY ARE VALUABLE TOOLS. IN THE FUTURE; I WILL RECITE FARS IN A MORE MATTER OF FACT WAY -- IF THEY ARE THREATENED; INSTEAD OF 'RECOMMENDING;' THIS DOESN'T LOOK RIGHT; WHY ARE WE HERE?