Smokers are not a protected class, and it is perfectly legal to discriminate against them in housing, in employment, in restaurants, in any setting you please in the United States.

Of course at one time the same would have been true of gay people. Or black people.

It's a dangerous road to go down, discriminating against people.

I don't smoke, and I'm glad I don't smoke, and I was glad when the ban on smoking in pubs came in. But I think that there's a risk in stigmatising smokers as such - it even carries a risk, in time, of glamorising it as a kind of outlaw symbol of dissidence.