AN ACR B737 INBOUND ON THE CIVET ARR SAW WX AND WAS ENCOUNTERING TURB AND HAIL AND REQUESTED A DEV TO AVOID WORSE WX. THE FIRST APCH CTLR APPROVED THE DEV AND WHEN GIVEN A FREQ CHANGE THE NEW APCH CTLR TRIED TO TURN THE ACFT BACK ON COURSE. THE CAPT RPTR REFUSED THE CLRNC TO RETURN TO THE ARR OR TO TAKE THE CTLR'S VECTOR; INSTEAD DECLARED A WX EMER UNTIL HE WAS CLR OF THE WX. RPTR DIDN'T LIKE CTLR'S ATTITUDE.

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SIGMETS HAD BEEN ISSUED FOR SOCAL FOR TURB; ICING; AND HAIL TO 1 INCH. APCHING CIVET INTXN; WE WERE IN AND OUT OF CLOUDS; EXPERIENCING MODERATE TURB AND OCCASIONAL RIME ICING. THE SEAT BELT SIGN HAD BEEN ON ENTIRE FLT FROM LAS DUE TO TURB. WE GOT A LASHING OF HAIL JUST PRIOR TO CIVET. ON RADAR; AND VISUALLY; WE COULD SEE CUMULO NIMBUS ACTIVITY AHEAD ON THE ARR RTE. REQUESTED FROM SOCAL; AND GOT; PERMISSION TO DEVIATE S OF ARR; AND WHEN CLR AND ABLE; TO TURN TO 270 DEG HDG AND REINTERCEPT. THIS KEPT US OUT OF ECHOES. APCHING ARNES; NEXT CTLR TOLD US TO MAINTAIN 12000 FT AND TURN TO HDG 290 DEGS. THIS WOULD HAVE PUT US RIGHT INTO A LARGE CELL; SO FO TOLD HIM WE WOULD BE UNABLE DUE TO THE WX; AND ASKED TO STAY WITH PREVIOUS CLRNC. HE CAME BACK AND ORDERED US TO TURN TO 290 DEG HDG. I THEN ATTEMPTED TO EXPLAIN ABOUT THE WX THERE; AND THAT WE COULD NOT FLY INTO IT. HE SAID HE HAD NO WX AND THAT NOBODY ELSE HAD RPTED ANY. I TOLD HIM THAT WE WOULD BE UNABLE TO COMPLY WITH HIS HDG DUE TO THE WX; SQUAWKED 7700; AND REMAINED S OF CUMULO NIMBUS. APPROX 10 MI W OF ARNES; WE BROKE INTO CLR; TURNED TO 270 DEGS; AND RESUMED ARR. SOCAL CTLR'S HANDLING AND ATTITUDE WERE EXTREMELY POOR. NEITHER OUR COMPANY PROCS NOR MY JUDGEMENT WILL ALLOW US TO ENDANGER ACFT AND PAX BY FLYING DIRECTLY INTO ACTIVE CONVECTIVE WX; ESPECIALLY WHEN ATC DOES NOT SEEM TO HAVE A CLUE WHAT GOES ON OUTSIDE THEIR BUILDING. IN ACCORDANCE WITH OUR PROCS; I EXERCISED CAPT'S EMER AUTH TO AVOID SUCH ENDANGERMENT.