The Alaska state constitution has a "right to privacy". Some guy challenged the state marijuana laws (I think in 1973, 1975) saying that he had a right to smoke in the privacy of his home. The Alaska supreme court agreed, and placed the limit at 4oz. (personal use amount).
The University of Alaska did a survey in 1988 of teen marijuana use and found that teen use was double the lower 48.
The voters went ballistic and passed a referendum to go back to the original laws. Teen use equalized.
I hope that answers your question of "What is the harm of one person doing drugs in thier home?"
What happened in the city of Chicago when it became illegal to produce or consume booze?
Uh, people caused damage numbered in the billions, rapes and violent crime were at an all time high, it was mass hysteria and the crumbling of every decent moral institiution, and wasn't good for the environemnt either?
During Prohibition, were the people demanding the legalization of just wine? And what if only wine were made legal and the rest of the alcoholic beverages remained illegal?
Would you expect wine legalization to solve any of the problems caused by Prohibition? But you fully expect marijuana legalization to, don't you?
You failed to point out any harm done by those teens smoking pot. Other than to themselves. Still no harm to anyone, certainly nothing more harmful than smoking tobacco, which is legal of course. Or caffeine for that matter, we happily shove caffeine down the throats of our teens in huge doses (think mountain dew).
If it's health problems you are concerned about, then why is tobacco legal? Not to mention, that with legalization will come better and more healthy delivery methods, smoking pot is a poor delivery method. THC is the safest therapeutic drug known to man. How many THC overdose related deaths were there in the last 10 years? Want a hint? Less than 1.
Also, of course you will have an increase in use initially, it's called novelty. Take a look at cigarette smoking in the US today. Is there anyone who would recommend you start smoking?
Your use of Wine instead of harder drinks misses the point. You are still dealing with the same drug, alcohol. THC can come in a large verity of forms and different potencies. I'm advocating that we legalize all of them.