His parents would appear to be taking the stance that they haven't the right to stop him from doing what he wants to his own body. After all, his body is his own property. While you may not agree with their ethics, it doesn't make them bad parents.
Personally I intend, if I ever have children, to educate them about it. Awareness is a better virtue than ignorance, particularly as my children would, given the way society is, be involved with it at some point anyway. It's the same concept as alcohol: as a guardian you don't allow your child to drink, but as they leave their mid-teens and start to have a mind of their own you can do little about what they want to do. The only thing you can do is educate them while they're still willing to listen, so if you're going to give such a blunt refusal to your children, I pity them.
As for rape, that's reductio ad absurdum. Use of weed pertain's to one's self. Rape directly harms another, and has vast moral implications. Don't take my stance the wrong way; if I'm ever a parent I intend to be firm about what I do and do not want in my household. I'm not interested in taking in passive weed smoke when I don't want to, any concertgoer will tell you it can affect you even though it's passive. You seem to believe that ignorance is the best way to stop it, but provided they then become exposed to it the situation simply gets worse than it could be, and you can easily be labelled a hypocrite.
At a young age his body isnt his to do to as he pleases...
Taking the fact that hes still living with her parents Im guessing he is still young. His mind hasnt fully developed and he is unable to make sensible dessions on his own. This being said there are people under then 18 that are able to, but the fact that he has chosen to smoke up shows you hes not making a wise choose.
Parents allowing the child to do something legally is just stupid. Yes its not as bad as drinking, but at a young age its also illegal to drink, so he shouldn't be dong either one of them, and a good parent would try to prevent them from doing such a thing, not give him the thumbs up and let him blaze himself silly.
If he is still in school it will effect all sorts of things and may have a great impack to what his life will turn out to be..

















