Definitely go with a vapor barrier, polyethylene sheet is cheap and installing it before the drywall goes on is simple. Some info from my day job...
Warm air is more humid and tends to "drive" to cold, less humid air. Drive direction in summer is exterior humid air migrating toward the air-conditioned, cool interior. In winter, the opposite occurs. (This despite us saying that interior heat dries air, and cold winter fronts are moist. Drive in winter is still inside to outside.)
The primary point of a vapor barrier is that it keeps warm humid air from migrating half way through the insulation and condensing when it gets to a cooler temperature at the dew point. Over time, this can destroy the insulation (when the dew mattes it together or when it freezes) and create a fabulous place for mold to grow. In NC, this can happen in either direction, summer or winter.
A secondary purpose of a vapor barrier is to prevent air infiltration into air conditioned spaces. The process of air conditioning is actually the same as de-humidification. Cooling by blowing air over cold coils dries the air, condensation on the coils is the result. (Which is why you want your air conditioner on when you are de-humidifying your car windshield in the winter, with the heat on.) This takes a LOT of energy. Without a vapor barrier, all the de-humidification (and resulting cooling) is wasted, humidity from outside simply migrates, or drives, right back into the space.
These reasons are why the vapor barrier should go just under the drywall in NC. A light weight polyethylene sheet does the job, with plenty of attention to seals at laps.
Now for the caveats.
The reality is that sealing a home is nearly impossible. It is necessary to vapor barrier every square inch of wall, floor, and ceiling/roof or little benefit is gained. And there are those corner conditions (like at rim joists) that usually have no barrier. How many drywall nails/screws go through the barrier? Plus craftsmanship issues where a portion is forgotten or poorly constructed. Then if your windows are like mine, you can pass paper between the cracks at the jambs, heads and sills. Doors are equally notorious after a few years settling. And if you are like our household, the doors open and close so often in the summer I feel like I'm cooling the neighborhood!
Opening windows on summer nights completely negates all the work the AC did during the day time, the humidity rushes in and infiltrates drywall, wood, cloth, carpet, etc. (It takes more than a day to re-extract it all.)
Knowing the general issue with leakage, many building science people now recommend vapor
permeable barriers on commercial buildings. These are complex chemical coatings that keep water out but let drive be unrestrained to allow pockets to dry out occasionally and resist mold growth. But we're talking about a completely different type of construction, from windows, roof, envelope, HVAC systems, etc., to the barrier itself. So I don't think these apply to residential type construction.
If it was me, I'd go with the vapor barrier. Even if it is only on a portion of the wall, it will slow down drive in the immediate vicinity of the insulation and buy at least some slowdown of migration for energy savings to the degree that it can be installed.