E-145 CREW WAS INTIMIDATED BY THE ACR CHIEF PLT TO OP A FLT IN FORECAST SEVERE ICING CONDITIONS. THE FLT ENCOUNTERED SEVERE ICING.

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ENRTE FROM PIT TO GSP; WE RECEIVED AN UPDATE FROM ZID THAT A SIGMET WAS NOW VALID COVERING SEVERE ICING CONDITIONS DIRECTLY OVER OUR DEST; GSP. IT RPTED SEVERE ICING BELOW 5000 FT. OUR COMPANY CHIEF PLT TOLD US THAT BECAUSE NO PIREP WAS MADE ABOUT SEVERE ICING CONDITIONS THAT THE SIGMET WOULD NOT AFFECT US. OUR GENERAL OPERATING MANUAL STATES FLT INTO KNOWN SEVERE ICING IS PROHIBITED. WE DISAGREED WITH THE INTERP OF OUR CHIEF PLT; BUT HE AND FLT CTL ASSURED US HE WAS RIGHT. WE CONTACTED CTR; GSP APCH; AND GSP TWR TO CONFIRM CURRENT WX CONDITIONS AT THE ARPT; RECEIVE ANY MORE PIREP UPDATES; AND CONFIRM THE SIGMET WAS STILL VALID. ALL PIREPS STATED LIGHT TO MODERATE ICING FOR GSP. WE DECIDED TO TRY THE APCH; AND WE ENCOUNTERED SEVERE ICING 3-4 MI OUT ON THE APCH TO RWY 4. WE EXECUTED A MISSED APCH IMMEDIATELY AND DIVERTED TO CLT. I WAS THE PNF FROM PIT TO GSP; AND AFTER WE WENT MISSED; THE CAPT DEALT WITH RADIOS; FLT CTL; ETC; AND I FLEW THE ACFT TO CHARLOTTE. OUR CHIEF PLT TRIED TO AFFECT OUR DECISION TO CONTINUE. HE ALMOST SUCCEEDED. I WOULD LIKE TO SEE CLR INTERPS ABOUT AIRMETS AND SIGMETS BEING CONSIDERED FORECAST WX.