Here is how the conversation goes.
Idiot: If your not addicted to marijuana then you can quit right now.
Me: I use it for medical reasons and do not want to but have and can if I need to:
Idiot: So you won't quit therefore it proves that you are addicted.
No it does not prove I am addicted. This argument proves you have no clue what your talking about. This argument is an example of circular reasoning and somewhat of begging the question. You could use this argument for anything. Television, food, driving, and even sex.
Try this, change marijuana with any activity you enjoy doing. Then read the argument with the new activity and realize how rediculous it sounds. It sounds just as rediculous to people who smoke marijuana.