Your are correct sir. No conclusive studies can prove this, but... I have a friend who just turned 45, he smoked cigarettes for 20 years, but quit ~ 7 years ago, prior to a major surgery. He continues to smoke pot daily, as a medical user for his severe arthritis.

 Recently he had a lung exam and at the end his doctor said his lungs were functioning completely normal and they're apparently just as pink as if he never smoked... Now I'm sure everybody's different, but damn especially after smoking cigarettes and weed for that long his lungs would be fucked, but alas they are not