I agree that children should be discouraged from having such social circles.
I still believe that the most persuasive argument against marijuana, to children, and even marijuana users, is that it makes them dull and dim-witted.
Most children and adults want some sharpness and clarity in their lives. To do things, meet people, learn and experience their times. Marijuana just slows things down, so they do less, have less fun, miss out on things, and lead a ‘meh’ kind of life.
This actually makes a great deal of sense, where scare tactics and dire warnings fail.
Scare tactics? As in, misrepresenting the consequences of "responsible" marijuana use?
Satchmo -- Louis Armstrong -- was well known to be a lifelong pot smoker. Michael Phelphs sure as heck knew his way around a bong (judging by that hilarious clandestine video of him taking a huge toke at some party) long before, and long after he became the most decorated Olympic athlete of all time (he's got 22 medals).
Boy, they sure led "meh" lives!
The best way to steer kids away from drug ABUSE is to tell them the truth. The best way to steer kids into doubting your honesty and therefore your wise counsel, is to tell them soft lies such as the one that all social/recreational pot smokers are dullards, while social/recreational drinkers can and do function just fine as long as they're responsible.
The reality is that it has zero to do with the substance, and everything to do with the moral priorities of the user.