>Many times someone from a certain religion might cost an employer more than someone who doesn't need religious prayer breaks. But legally employers can't act on that.

They can't act on that, specifically because we have a law that prevents them from doing so. Religion is a "protected class" in employment, along with a few other things (race, gender, etc.).

Smoking is not a protected class, so employers are free to discriminate all they want. Do you really want to spend your time writing to Congress to have them pass a law making smoking a protected class?

>having kids, etc)

I'm not sure, but I think having kids is already a protected class. If it isn't, it probably wouldn't be that hard to get that law passed. Getting it passed for smokers would not be so easy. Personally, if Democrats took this up as a major campaign issue, instead of focusing on more important things, I probably wouldn't vote for them any more.