Why can't we have more laws and more education? You're mixing things together here. The OP brought up a question. He also said that his solution was to close his window. No one advocated making what that particular smoker did illegal. It's just a tough situation that people were looking for a good solution to.
Yup, no one does.
Sorry, but the slippery slope argument doesn't work here any more than it does regarding same-sex marriage. You could say "Well, first we can't beat our kids, and next thing you know, we won't be able to have kids at all". The point is there are some things people shouldn't be allowed to do. We take them on a case-by-case basis. Making one thing illegal now because it makes sense doesn't mean that we're going to end up with 1984.
I'm sorry for your experience. However, I don't think that's typical. My cousin is special needs, and they rarely deal with social workers. And maybe it's just your particular social worker. Unless your house is in really bad shape, you don't have anything to worry about legally.
But I also don't see what this has to do with anything. There are two options:
1) We can just let parents do whatever they want with their kids without any rules.
2) We can set rules for what parents can do with their kids.
I assume we both support option 2. Then the question is just a matter of what is acceptable and what isn't, what we can tell parents and what we can't. There is already a line drawn. We can't beat our children. We can't subject them to horrible living conditions (at least not when we have other easy options). We can't lock them in the basement or a cage. The reasons for those are that they unnecessarily harm the kids. It's the same reason I can't beat you up and you can't shoot me.
Obviously, we need to keep out of parenting as much as possible, but there is a certain amount of checking up we have to do. All we're saying is that smoking in an enclosed place with children should be added to that list of things you can't do as a parent. Education would also be a good component.
And just to be clear, since I'm not sure it is: I am not advocating making smoking in your own house illegal, unless there are children in there. If that condition is not there, then have at it all you want.
Of course we can't do anything we want with our kids, I never said otherwise. We just can't dictate every little thing for people to do. As I said, it would be best if people did not smoke with their children in the house; there are a lot of things we shouldn't do with children in the house, people shouldn't feed their kids McDonald's everyday, either. I am saying that it takes too many resources that we don't have to go around door to door checking that people aren't doing these things (I know I am being a little extreme in this argument, and I am not saying this has happened or will happened).
The fact remains is that my husband and I did not abuse our special needs sons, we didn't neglect them, we didn't smoke around them (neither of us smoke at all, so this was easy), we didn't leave them alone to burn down the house, we keep the house reasonably clean, yet we still had social workers dropping in unexpected. I have heard atheists say they don't want people coming door to door to proselytize, and I say that social workers dropping in unexpected is very much the same thing as a religion coming to your home and proselytizing.
I know it seems contrary, but I do understand what you are saying. But I just can't advocate a nanny state. If there is a reason to come over, that someone is abusing their child is OK, but otherwise, it is against our privacy.