I hate smoking, but think this is rather ridiculous. While I see what they want to do, until they also refuse to hire heavy drinkers and overweight people they have no moral grounds to stand on. Smoking is easy to go after, and that's the only reason we're seeing this.
It's not ridiculous at all. First of all, your argument is sort of ridiculous, no offense. Why? Define "heavy drinker". You cant test someone for that. And as for the obese or overweight analogy employers are moving towards more of a wellness component and forcing employees to address their weight issues. Even then, there are legitimate reasons why someone is overweight sometimes. But drinking in moderation isn't an issue. Smoking is. There is NO smoking in moderation. One puff or a carton is bad for you period.
But to give more of a reason for the smoking issue is this, call it Fact One; It has been proven over and over again that smokers are less productive. The empirical evidence that smokers have lower productivity over working years is fairly strong. They are less productive because they miss work more frequently (absenteeism) and because their smoking-related health conditions (shortness of breath, cardiovascular conditions, cancer, COPD, etc, etc) may affect their ability to perform certain kinds of jobs (presenteeism). Even if the company does not pay sick leave, the disruptive effects of more frequent absences in jobs that require teamwork (such as hospital nursing) will probably lead to increased costs to employers. Not to mention, you can see smokers huddled up all over the place at any given time taking their "smoke break'' outside. I once knew a company who fired a smoker for lack of productivity over this. The employee sued, and we had it tossed easily because the employee used the argument that they only went out for a smoke when they took their restroom break. So the employee didn't think it was a "big deal", and they were being denied their restroom break rights (I kid you not). Other employees went only to the restroom, thereby taking much shorter breaks on total than the smoker did. Not to mention it was an at-will state, and smokers (thank God) are NOT a protected class under federal law.

Fact Two, smokers have higher medical costs. Smokers have higher average health care costs than non-smokers, other things being equal. (They may have higher life insurance costs as well.) Almost all job-related insurance in hospitals and most other places is experience-rated or self-insured. Even if employee premiums for health and life insurance are not adjusted for smoking status, the fact that medical costs will increase for firms or occupations with larger shares of smokers means that there will be offsetting reductions in wages. Companies have less and less to spend on wages as a result.
Consumers and coworkers may prefer non-smokers. In face-to-face interaction with workers, buyers or consumers of health care may have preferences about behaviors or appearance of workers; attributes that buyers regard as negative will depress total compensation and wages, because it will adversely impact the companies sales overall. In contrast, for occupations and industries where consumers see only the final product (a manufactured good, a piloted airplane) there should be no such negative effects. In hospitals especially, this is important because healthcare overall is getting extremely competitive across the country. Insurance companies are forcing their members to become much more savvy about how they spend their healthcare dollars. Imagine the impact on a cancer patient who is being told by their doctor to absolutely refrain from smoking, and they show up and the girl/guy who pushes the poison into their arm reeks of cigarette smoke. I personally would probably feel like, "How can I trust THIS place to save my life, when they can't even get their own employees to stop smoking." People notice these things. It's not just about curing people. Hospital systems recognize they need to lead by example to capture those dollars more and more.
Personally, I think we should ban cigarette smoking. While I'm in favor of medical marijuana, I abhor tobacco use of any kind. I smoked for nearly 21 years. Worst thing I've ever done. I quit on St. Paddys day while waiting in line to see DT at the Riv in Chicago. That was in '02 I believe. I still worry about walking into my doctors office someday and needing a chest x-ray and they tell me I have cancer. I wish someone had kicked my ass when I started smoking. Like rats, or Ebola, there is NO value to smoking (except for the people in tobacco, and treatment of smoking related disease). And yeah, I know we ex-smokers are the worst anti-smoking advocates most of the time. There is a reason for that.

EDIT: I'll also add this. I own part of a restaurant, and we don't allow smoking there. We don't allow workers to meander outside and smoke either. In fact, we even have policies about strong odors, or colognes/perfumes. We don't want any strong odor impacting or effecting our guests in any way. Our service should be excellent, but an otherwise neutral experience for our customers. It does make a difference.