You don't slur your words when you're high. Alcohol is just as much a drug as marijuana, and its effects are infinitely worse across the board. First, marijuana is not addictive. I lived with people and watched plenty of friends go from being occasional to full-time users. But I'm convinced they have all demonstrated a mental addiction and not the physical one that almost all other hard drugs, and most notably alcohol, lead to.
Alcoholism can run in one's family and make a person much more prone to addiction than others.
People can get addicted to anything, so when I read about some guy who got high every day for the last 40 years, I'm not impressed. And I can match this case with at least 10 cases of alcoholics who are much worse off now after 40 years of excessive drinking. The real point here is that certain people are simply prone to addiction. The people who are mentally addicted to marijuana have a weakness for it maybe they aren't motivated to do something, so they'd rather smoke. Nevertheless, I've seen a few friends become addicts, and it is a sad and tragic process.