I know a lot of people who smoke weed (some without children, some with, including my parents), but only once or twice a year, if even. Done occasionally, I don't really see it as a problem. I used to smoke weed the odd time, but in the past couple of years have found that it makes me a moany, depressive pain in the arse, so don't touch it any more. I really don't see it as any more of an issue than a couple of bottles of wine occasionally, at a party or something.
However, DP and I have a friend who has been smoking every day for the past few years. It wasn't a problem at first, but lately it has made him horribly irritating and navel gazing and antisocial. When he comes around for dinner with some other buddies he just gets stoned and falls asleep at the table. When the three of us hang out, all he wants to do is smoke, eat bacon fries, stick on a shit movie, stare vacantly at the screen and talk self-indulgent bollocks. We used to have a great craic, talking shite and laughing and playing board games over a few beers, but he has become a giant headwrecker. We have tried to convince him to smoke less, but he refuses to do so. Oh, and then there was the night that he brought his dodgy-as-fuck dealer to our house, which I had a huge problem with. So, we see a lot less of him now. Sadly (for him), many of his other friends seem to be of the same mind, and are also seeing a lot less of him. What is worse is that he is usually so stoned, he doesn't care.
I do agree that it should be legalised though, then it could be regulated and generate tax revenue.