I don't think there is any GMO sweet corn.
Only field corn, grown for grain, has the Roundup Ready and/or the BT gene. The biggest effect has been that because of this technology, the chemical footprint left by production is now only a fraction of what it was before. One or two applications of glyphosate, which isn't soil active at all, has replaced multiple applications of atrazine, which remains in the soil almost indefinitely, and leaches down to the groundwater. Bt, or bacillus thuringiensis, a biological rather than chemical pesticide that occurs naturally, has replaced multiple applications of organophosphate insecticides. The BT gene in corn means the corn is no longer sprayed with these organophosphates.
There is a lot of misinformation, myths, and outright lies out there concerning GMO crops.