FACT Mold is common. Code requires that in the event that mold occurs in the drywall during construction the contractor is required to remove the mold by cleaning and/or sealing with an appropiate sealer. Appling the finish generally is considered a sealer by code anyway. It cuases no danger to anyone and as long as the mold is sealed to prevent its growth. Mold requiresa dampness to grow and cannot grow in applied drywall compound. Now many contractors don't bother washing the walls and still I have never seen any problems. Most good painters when seeing mold in the finish (streaks of black or green) will automatically seal the areas affected anyway.
Mold in rough drywall is no problem. People telling you otherwise are just trying to make a buck. REMEMBER IN A FINISH HOME MOLD NEEDS THE PRESENCE OF DAMPNESS TO GROW!!