POTENTIAL CONFLICT WITH OPPOSITE DIRECTION TFC DSNDING TOWARDS OCCUPIED ALT. NORAC TFC.

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APCHING THE ARD VOR AT 11000 FT MSL ESTABLISHED ON THE NANCI 5 ARR TO LGA; APCH CTL ADVISED OF VFR TFC AT OUR 12 O'CLOCK; 10 MI AND APPROX 11500 FT MSL NOT CONFIRMED. WE SHOWED THE TFC ON OUR TCASII 300 FT ABOVE AT OUR 12 O'CLOCK LESS THAN 10 MI CLOSING RAPIDLY (OPPOSITE DIRECTION). WE WERE BTWN LAYERS IN AND OUT OF THE CLOUDS AT 11000 FT AND THE BTWN THE LAYERS WAS LESS THAN 500 FT. ONCE THE TFC WAS WITHIN 5 MI ON OUR TCASII IT STARTED TO DSND INTO US AT WHICH TIME OUR TCASII ISSUED AN 'RA' TO CLB IN EXCESS OF 2000-2500 FPM WHICH WE DID AS WE STARTED A TURN AWAY FROM THE TFC TOWARDS THE ARD 078 DEG RADIAL E OF ARD. ONCE LEVELED AT 12000 FT MSL THE TCASII ISSUED A CLR OF CONFLICT AND WE RETURNED TO 11000 FT MSL. ATC WAS AWARE OF THE SIT AT ALL TIMES. THIS CONFLICTING TFC WAS OPERATING VFR IN IMC CONDITIONS OPPOSING THE TFC ON AN ESTABLISHED ARR RTE INTO LGA. A HAZARDOUS PRACTICE AT BEST. THIS IS NOT A FIRST CONFLICT WITH VFR TFC IN THE NY AREA. COMMUTER ACFT SEEM TO MAKE IT A GENERAL PRACTICE TO OPERATE IN AND AROUND THE NY AREA VFR IN AN ATTEMPT TO SAVE A COUPLE OF MINS. IN MY OPINION; AIRLINERS OF ANY TYPE SHOULD NOT BE ALLOWED TO OPERATE VFR IN AND AROUND HEAVILY CONGESTED AIRSPACE.