VFR OPERATION WHEN VISIBILITY WAS REDUCED TO 2 PT 5 MILES.

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I TOOK OFF ON A TRNING FLT WITH MY STUDENT FROM SBY. THE ACFT WE USED WAS AN SMA. AT TKOF TIME THE WX WAS 250-OVCST 3 MI IN HAZE. MY INTENDED AREA OF OPS WAS A PWR LINE 4 MI S OF THE FIELD AND BTWN 600-800' AGL. NO FLT PLAN WAS FILED AND WE WERE MONITORING THE AAS FREQ. AFTER 20-30 MINS OF GND REFERENCE MANEUVERS WE TURNED N TOWARD THE ARPT AND CALLED FLT SVC FOR AN ARPT ADVISORY; WHICH HE GAVE. IN ADDITION TO THE ADVISORY INFO; HE TOLD US TO 'HURRY ON IN HERE; WE'RE GOING TO CALL IT 2 1/2 MI IN HAZE.' AT THAT POINT I WAS WITHIN A MILE OF THE FIELD AND HAD IT IN PLAIN VIEW. UPON XING OVER RWY 14-32 ON OUR XWIND LEG FLT SVC CALLED BACK AND SAID; 'CONTACT PATUXENT APCH FOR A SPECIAL VFR.' I FELT IT WAS A LITTLE LATE TO BE CALLING APCH CTL FOR A SPECIAL VFR WHILE ON DOWNWIND OF MY LNDG APCH; BUT I CALLED ANYWAY. I WAS ANSWERED BY PATUXENT APCH WITH A PERFUNCTORY 'ACFT CALLING PATUXENT STANDBY.' AT THIS POINT I WAS TURNING BASE TO FINAL; AND IF THE WX OBSERVERS INSISTED ON CALLING THE VIS 2 1/2 INSTEAD OF 3; I FELT IT BEST TO ARGUE WITH THEM ON THE GND INSTEAD OF 'STANDING BY' ON THE AIR. AFTER LNDG I CALLED FLT SVC AND WAS TOLD THAT PATUXENT WANTED TO VIOLATE ME FOR BEING IN THE CTL ZONE W/O IFR OR SPECIAL VFR CLRNC. DURING THE ENTIRE 20-25 MIN FLT WE NEVER LEFT THE CTL ZONE. THERE WERE ABSOLUTELY NO CLOUDS IN THE AREA; ONLY HAZE. THE VIS IN MY OPINION HAD NOT DETERIORATED AT ALL. WE DID NOT SEE; MUCH LESS HAVE ANY CONFLICT WITH ANY OTHER ACFT DURING THE FLT.