In theory, the Sons want to protect their homeland... Charming. to the degree that they see a vice as tolerable, they allow it. They're involved in pornography too, after all. But even the gun dealing, etc. they see as a way to protect charming. When you start dealing in mass drug distribution, the quality of life in the target area tends to decrease. SAMCRO certainly don't want people on corners or at schools trying to sell drugs. The legal system also has considered drug busts quite "glamorous". It's why we always see the big drug busts on the TV and newspaper. My take is SAMCRO just considers it more trouble than it's worth. Or at least they did.

If we think back to the movie The Godfather, didn't they have basically this same attitude? With all the criminal activity the Corleone family was involved in, Don Corleone didn't want any part of drug trafficing. Charming's kind of a throwback.