I really don't think a cannabis addiction can be classed as the same life ruining addiction that alcohol is. Maybe because of it's legality it can ruin lives but the parent was specifically talking about after it became legalized.
"Smoking marijuana is more dangerous than smoking cigarettes, experts say. The tar in joints contains a much higher concentration of the chemicals linked to lung cancer compared with tobacco tar. And smoking marijuana deposits four times more tar in the lungs than smoking an equivalent amount of tobacco, according to the National Institute on Drug Abuse."
http://www.cnn.com/2014/01/20/health/marijuana-versus-alcoho...
One thing we can expect with legalization is that consumers will be better informed about those alternatives.