IMO, there are two reasons for that attitude, one of which is really not a reason and the other could be.
One is that smoking has been accepted by society for a very long time and some people have a problem accepting change. I don't consider this as a valid reason for having that type of attitude.
The other reason is that smokers, for the last however many years, have been demonized to the point that many will treat a smoker as a second, or third, class citizen, not entitled to the same rights, liberties, or courtesies as any other citizen.
They are reviled, set upon physically in venues where smoking is allowed, called worse names than some mass murderers, have legislation forced upon them using junk science as a basis for said legislation, and even have television commercials that tell other people they are not normal everyday folk that feel, think, or have thoughts beyond, "Where's the next cigarette coming from".
This, IMO, is a reason for the attitude. It's kind of like, "If I'm going to get the results anyway I might as well play the part."
I'm not saying it's right but I can, at least, understand it.
I DO try my best to avoid the "IN-YOUR-FACE" attitude until, and unless, I am treated to that attitude by someone else.
When a small minority, the true anti-smokers, use junk science to force legislation, smoking bans, on another minority, smmokers, it is a blatant misuse of the legislative system.