A CL65 FLT CREW RETURN LAND WHEN THE WX AT DEST ARPT IS BELOW LNDG LIMITS FOR FLT AFTER DEP FROM PIT; PA.

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I WAS ENRTE BTWN PIT AND ERI AT 17000 FT MSL. THE FLT WAS BLOCKED AT 18 MINS. I PROCEEDED WITH THE IN-RANGE CHKLIST AND COPIED THE CURRENT ERI WX. THE ATIS AT ERI INDICATED A 200 FT CEILING WITH RVR OF 2400 FT FOR RWY 6 (RWY 5 BEING THE ACTIVE RWY). THE ILS RWY 6 MINIMUMS AT ERI ARE RVR 4000 FT OR 3/4 MI VISIBILITY. WHILE LOOKING AT THE HARD COPY WX TAF FOR ERI ON BOARD THE ACFT; I NOTICED THAT; FOR MY SCHEDULED TIME OF ARR; THE MAIN BODY OF THE FORECAST INDICATED A 1/2 MI VISIBILITY AT ERI WITH A 'TEMPO' INDICATING 3/4 MI VISIBILITY. THE LATEST HARD COPY METAR INDICATED THAT THE VISIBILITY IN ERI WAS 3/4 MI. WHILE REVIEWING ALL APCHS AT ERI; I NOTICED THE LOWEST SUITABLE LNDG MINIMUMS REQUIRED 3/4 MI VISIBILITY. WE DIVERTED TO OUR ALTERNATE ARPT WHICH WAS PIT. UPON ARR AT THE GATE; I PHONED OUR DISPATCH CTL AND SPOKE WITH MY ASSIGNED DISPATCHER. HE INFORMED ME THAT WHEN HE 'BUILT' OUR FLT RELEASE; THE FORECAST AT ERI HAD INDICATED A VISIBILITY OF GREATER THAN LNDG MINIMUMS. THE HARD COPY TAF I HAD ON BOARD THE ACFT WAS AN AMENDED (NEWER) FORECAST. PRIOR TO DEP FROM PIT; I FAILED TO NOTICE THE LOWEST SUITABLE LNDG MINIMUMS FOR ERI. DISPATCH OF THE ACFT REQUIRED THE VISIBILITY TO BE 3/4 MI IN BOTH THE MAIN BODY AND 'TEMPO' SECTION OF THE TAF FORECAST. NOTICING THAT ERI HAD 2 ILS APCHS; I ASSUMED THAT THE LOWEST VISIBILITY WOULD NEED TO BE 1/2 MI. FACTORS THAT CONTRIBUTED TO THIS COMPLACENT OVERSIGHT WERE THAT WE WERE RUNNING BEHIND SCHEDULE AND WERE RECEIVING PRESSURE FROM COMPANY DISPATCH TO 'MOVE' THE FLT ASAP FOR COMPLETION FACTOR; FEAR OF REPRIMAND IF WE WERE LATE; AND THE ASSUMPTION OF COMMON ROUTINE THAT ILS APCHS REQUIRE 1/2 MI VISIBILITY. POSSIBLE CORRECTIVE ACTIONS: THE PRESSURE TO PERFORM OR FACE DISCIPLINARY ACTION INCREASES THE POSSIBILITY OF MAKING INADVERTENT MISTAKES. SAFETY SHOULD BE STRESSED MORE THAN ON-TIME PERFORMANCE.