"What about the argument that Marijuana is a 'gateway' drug that leads kids to harder stuff?"
That argument is a correlation argument. For example, "Ninety percent of heroin addicts have a marijuana history. Therefore, it is safe to say that marijuana is a 'gateway' to heroin addiction."
Sounds acceptable, at first hearing? Only if you are a deck crewman on a carrier during launch time.
Here's another version of that first argument, " Nearly 100% of heroin addicts have a milk history."
Still think that correlation argument sounds acceptable?
Maybe I didn't make my sarcasm clear in the rest of that post. I agree with you.