You and a few others have outlined some very important and overlooked points about substance abuse, drug addiction, and (in a broader, latent scale) mental illness. Well done.
For the record, nobody here is saying they are okay with Kassian having an addiction. Nobody is giving him a free pass. Nobody is making excuses.
What people are saying is there are a lot of factors that make this a complex issue, and judging people as good or bad based off of bad decisions demonstrates ignorance. Because the fact is, there are plenty of people who DO suffer from a predisposition to addiction and they make the right decision to stay away from the addictive substance. Kassian violating the stage 1 rules suggests he hasn't, though we don't know to what degree that's been violated.
The point is, it IS possible for someone to make a bad decision AND for outside viewers to acknowledge there's a problem which may have influenced that bad decision. Any time you have someone addicted to substances, hoarders, compulsive gamblers, spenders, people with Internet or gaming addictions, you should be able to acknowledge there is something more complex than "makes bad decisions/bad person."