A major caveat is that vaping is a big problem now. I believe it is marginally (or maybe even substantially) safer than traditional smoking but it’s still just peddling a nicotine addiction to youngsters.

Vaping nicotine is probably about as harmful to health as chewing nicotine gum; and vastly less harmful than smoking.

It is certainly a way to take an addictive drug. It is also an extremely convenient one, which makes it more likely that people will use it more heavily. (See also the rise in the popularity of cigarette smoking after the invention of the rolling machine: convenience leads to more consumption.)

However, most of the direct health harms of smoking aren't from the nicotine; they're from everything else that comes with it --

• solid smoke particulates
• unburned and partly-burned resins ("tar")
• carbon monoxide

None of these are in the vapor produced by e-cigarettes.

Inhaling smoke is bad for lungs; no matter whether that smoke is from tobacco, another herb, a forest fire, unsafe industrial equipment, a coal-fired power plant, or a fireplace.

Nicotine itself is not carcinogenic, although it does constrict the lung passages which makes it harder for the lung to clean itself. Chronic use of nicotine vapes may be expected to cause some amount of emphysema due to this chronic constriction. But it's not gonna cause the massive amount of lung cancer that smoking does, because it just doesn't contain the high concentrations of carcinogens that cigarette smoke contains.

(I do not use nicotine at all, however I greatly prefer to be around people vaping than around people smoking.)