Carla,
Nice job!
I would include the entire 1 Cor 5:11 scripture immediatelly after their botched up wt quote (as a basis for the shunning) where the full text does not have any [or guilty of another gross sin] verbiage and is quite explicit as to who are we not to have contact with: ..."quit mixing in company with anyone called a brother that is a fornicator or a greedy person or an idolater or a reviler or a drunkard or an extortioner, not even eating with such a man".
Put an emphasis on how they twist the scripture to support their cause.
-Yan