I'm torn on this one.
On the one hand, I don't want to be fired for legally doing what I damn well please in my own home. Getting fired sucks. Been there...and for less of a reason.
On the other hand, employers are people with rights, too. Were I an employer, you can bet your ass that I would zealously fight for my right to legally run my business the way I see fit.
Not all discrimination is illegal. Not all discrimination is bad. Any one of us who ever applied for a job and didn't get it, was discriminated against...presumably in favor of someone more qualified. And I'm sure we all seen employers discriminate against tardy people, lazy people, and the perennially stupid. Let's say I have an employee who is an outspoken member of the KKK. He's got his freedom of speech of course, but what about my freedom of association and a right not to risk having his choice of speech affect my business? I live in a work-at-will state. He's outta there.
Now as a society, we've drawn the line at certain kinds of discrimination...and rightly so, IMO. But why should the government similarly protect us smokers? We know there are risks and consequences attached to our decision to smoke, yet we choose to do so. Why should the government shield us from those consequences and allow us to burden employers with additional costs that result from our personal choices? I'm havin' a bit of a hard time with that. But I also concede and agree that if one risky behavior is to be disfavored, one can quite rightly make the case that other, riskier (or more costly) activities should be discouraged.
Here's another thought: let's say I or you or a friend decide to open a kick-ass cigar bar. Me, I'd "discriminate" in favor of smokers. I'd want to hire people that smoke cigars, know cigars, and have a passion for 'em. But if a new law were passed to say that employers couldn't discriminate against someone because they smoked, I'm guessin' that I likewise couldn't discriminate against potential employees because they don't.
That would suck, too.