To understand why electronic cigarettes have such passionate advocates, you have to understand the libertarian ideology underpinning the devices. To technophiles, e-cigarettes are not just a solution to the global smoking crisis, they are a beacon of free-market innovation.

While the tobacco industry is a perfect symbol of everything wrong with capitalism, and a clear illustration of the need for government regulation to protect consumers, many vaping defenders see their industry as a public-health solution guided by the profit motive. It's capitalism operating to save lives.

There is one problem: E-cigarettes, on their own, don't appear to be very good at saving lives. If you really want to get smokers to quit, you need to build an incentive structure.

Consider a study published this week in the New England Journal of Medicine. The study's authors took some 6,000 smokers enrolled in tobacco-cessation programs through their employers and randomly divided them into five groups. The first received information about the health benefits of not smoking and motivational text messaging. The second received free cessation aids, such as nicotine patches or pharmacotherapy and, if those failed, free e-cigarettes. The third received free e-cigarettes upfront. And the final two received financial incentives - worth up to $600 - if they kept from smoking.

The result six months later? Those receiving financial incentives were up to three times more likely to quit than those given free e-cigarettes. And while the quit rates for those given e-cigarettes were higher than other cessation aids or from the group that only received information and motivational texts, the authors note that the difference was not significant.

The researchers found similar results even when they focused on those who were motivated to quit when entering the programs. While about 5 percent of these smokers kept away from cigarettes for six months with the help of vaping, almost 13 percent were able to do so when given financial incentives.

Vaping advocates might object here to argue that even if e-cigarettes were relatively unsuccessful in making people quit smoking, they still may do some good by reducing the number of conventional cigarettes a smoker consumes. But experts warn otherwise. While e-cigarettes are considerably less harmful than combustibles, a recent report by the National Academies of Sciences, Engineering and Medicine explained that e-cigarettes could only be helpful in improving short-term health if they result in complete cessation of conventional smoking. In other words, it's all or nothing. You can't improve your health by smoking part-time.

Scott Halpern, the lead author of the NEJM study and a professor of medicine at the Perelman School of Medicine at the University of Pennsylvania, says the study provides some of the most robust data ever compiled on the ineffectiveness of e-cigarettes.

"We want this [study] to inform health systems and insurers - whether federal, state or private," Halpern said. "All those groups are offering these conventional cessation aids. What we find is that it's not money well spent."

In fact, Halpern and his team used the results of their study to calculate the cost of each intervention and found that financial rewards were far more cost-effective than e-cigarettes alone: While each successful cessation through e-cigarettes cost roughly $5,400, successful cessations through financial incentives cost only $3,400.

The lesson here is not to do away with e-cigarettes. They are, after all, a tool that can be used along with incentives. But it's doubtful that e-cigarettes can be successful in improving public health if they stand on their own. In fact, as other studies have shown, they may be doing more harm than good by introducing teens who have never smoked to cigarettes.

Clearly there is a need to regulate e-cigarettes to ensure they're not doing such harm. But they should also be part of a health campaign to specifically target smokers and offer them incentives to stop smoking. And, yes, that might someday include government programs offering money to people who are able to kick the habit.

That might rattle the libertarian sensibilities of some in the vaping community. But if they truly want to help people and free our society from the scourge of tobacco, science strongly suggests this is the right path.