I've never been a smoker myself, but I've known many, hung around many, and used to laugh off their secondhand smoke. But as I grew older, and as smoking became more socially frowned upon, my friends gave up their habits and I found that my life improved as well. No more stinky clothes or stinky hair just from hanging out with friends!
Here's the thing, though. I had a choice about whether I wanted to be around smokers or not. Kids don't always have that option. If their folks have a habit, they're going to be exposed to secondhand smoke, too. And that's not good.