MLG DESCENDING TOWARD DFW COMES IN CLOSE CONFLICT WITH SMA.

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WE WERE INBND TO SCY VOR ON THE 174 DEG R DSNDING TO 7000' OUT OF APPROX 8500'; CLRED FOR THE SCY 9 ARR TO CROSS BECKY AT 7000'. WE HAD BEEN GIVEN 1 TFC ADVISORY FOR TFC AT 2 O'CLOCK AND 4500' ABOUT 2 MINS EARLIER. NO CONTACT WITH TFC DUE TO HAZE AND SUNSET CONDITIONS. AT APPROX 4 DME A LIGHT SINGLE ENG; LOW WING; RETRACTABLE GEAR ACFT CROSSED OUR NOSE FROM RIGHT TO LEFT; HDG SW AT OUR ALT. THE RANGE WAS APPROX 600'. NO TIME TO AVOID OR TURN. WE INQUIRED WITH APCH CTL AS TO WHETHER HE HAD TFC AT OUR 9-10 O'CLOCK THEN. HE REPLIED NO. IT WAS JUST THE CASE OF HE WAS IN FRONT OF US AND GONE IN A MATTER OF SECS. SO THERE WAS NO EVASIVE ACTION NECESSARY. OUR LNDG LIGHTS WERE ALSO ON AT THE TIME. IT SHOWS VERY POOR JUDGEMENT FOR ANY VFR PLT TO BE FLYING OVER A CORNER POST TO THE DFW TCA PARTICULARLY AT AN ALT OF 8500'. ALSO; I THINK IT SHOWS THE NECESSITY OF KEEPING TURBOJET TFC ARRIVING AT LOVE FIELD AT 10000' OR HIGHER WHEN LNDG S INSTEAD OF DRIVING EVERYONE IN AT 7000' 40 MI FROM THE ARPT. ALSO; ANY ACFT FLYING ABOVE 3000' AGL NEEDS TO HAVE A TRANSPONDER WITH MODE C CAPABILITY.