There was a time when mental health professionals encouraged (or at least didn't discourage) the use of nicotine, as they considered patients who smoked to be self-medicating to help them cope. But when they assessed the benefits to the user, they found that most were related to relieving withdrawal symptoms rather than helping with the specific symptoms of their condition. IOW, smoking helped them feel better because they were no longer in nicotine withdrawal, not because they were coping with the mental condition better. So the feeling now is that patients should not use nicotine, and are better off in mental health terms by quitting nicotine. Withdrawal simply adds to the problems they're already facing.
People with depression are twice as likely to smoke, and those with schizophrenia are three times as likely to smoke. So the belief that the choice to smoke is an individual preference, and not tied in to broader demographic groupings and traits, is mostly false. It's also true that in almost every society, the less educated, unemployed, poorer, disabled, LGBT and immigrant/refugee communities have higher smoking rates than the national rate. From this, public health has deduced that smoking is a crutch of sorts, a means to help users cope with stigma and low self-esteem. Seeing as smoking is likely to draw dirty looks from non-smokers, thus driving down the smoker's self-esteem and increasing their sense of marginalization further, public health officials are keen for patients to quit and find other means to tackle their problems.
I don't think we are about to see public health officials laud the benefits of nicotine any time soon. If it turns out to have a positive effect on delaying the onset of Parkinson's and Alzheimer's, as has been proposed, mental health professionals will probably recommend medicinal application of nicotine as required rather than lifelong addiction. Somebody becoming addicted to nicotine in their teens, on the off-chance that it may help them delay Alzheimer's when they're in their sixties, isn't a valid argument for the medical fraternity.
This is the issue that the tobacco and vaping industries can't and won't answer. They have tried repeatedly to phrase the nicotine/smoking debate in terms of physical harms only. Public health isn't buying it. For them, the whole addiction cycle is, of itself, a health problem. Someone who is addicted to gambling or porn isn't going to get cancer from it. But it can wreck their lives in other ways.
My gardener came to me with a long face a few weeks ago. He is at risk of being evicted from his council home because he hasn't paid his utilities for ten years. It's not a huge amount but it's way less than he spent on cigarettes during that time. So it's a double whammy that his disposable income has gone towards a habit that is not only killing him but is depriving him of the ability to pay his bills. Even if he vaped instead of smoked and wasn't at physical risk from his habit, it's nevertheless still money that should have gone towards securing his home and providing for his family. Considering that smoking rates are highest in the developing world, and highest among the poor and unemployed, it's a major concern for public health. Financial wellbeing is part of mental health, and mental health is part of overall holistic health. It's a whole cycle, one can't just look at the cancer, COPD or heart disease risk.
In this sense, vaping is often its own worst enemy. I read an article once in which vapers suggested that airlines should allow vapers to vape during flights because, if they don't, it will increase the incidence of air rage among vapers. If I'm a public health official, I have to ask myself whether it's advisable for a large chunk of the public to be so hooked on a chemical that, if they are forced to go without it for just a few hours, it can induce air rage. Even if the addiction is not killing them, it can hardly be construed as a healthy state of being. This is why nicotine is being demonized: its effects extend beyond physical harms. If vaping wants to win over public health, they need to come with an argument for why addiction is a good thing. I'm not hearing anything in that regard.