On the subject of home growing, there seems to be a couple of points of confusion. First, home-grown does not necessarily mean grown indoors. I don't grow potatoes in my house, and I wouldn't grow marijuana in my house. For those who do want to grow indoors, it's a house plant that carries no more inherent risk than any other house plant. If you grow a lot of any plant indoors, especially if you're trying to create conditions to maximise your crop, you can get mould issues and such, but this applies to African violets just as much as it does to cannabis. Four plants won't be a problem.

The whole impaired driving thing is a red herring. First, there's no proof that stoned driving needs to be prevented; the evidence tends to support the conclusion that being stoned simply does not make you a more dangerous driver. Second, there are lots of people driving under the influence of marijuana now; there's no reason to think legalization will mean significantly more of them.