Maybe not the greatest analogy, but I'll liken the laws on smoking in enclosed areas to locks on our doors...they are designed to keep honest people out.
There is certainly legitimacy to your argument of degrees. Smoking in a car with the windows open is certainly not as bad as with the windows closed. But how do we determine the amount? Do you keep the window half open for one smoker and fully open for two? What about the guy that just barely keeps his pipe lit with wisps of smoke as opposed to a cigar guy that blows out billows of smoke? The reality is that you're visible in your car and you're in the public eye, and that, in my opinion makes you subject to the law.
As far as your own home goes, I believe that the US constitution as well as the Canadian charter of rights protects us from intrusion in our homes. It's a bit of a conundrum in that it both protects and infringes on certain individual's rights, but its still better than any other system.
I'll close with another "cliche". Smoking is definitely legal but, just because you have the right to do something, it does not make it the right thing to do.
I have yet to meet a pipe smoker that is not a reasonable person when it comes to these matters, but its also important to have an open discussion and allow all views to be heard. Lets keep talking