Nicotine itself is bad.

Yes, it's probably much better for you to not inhale hot smoke particles in your lungs and all the other ancillary chemicals from cigarettes, but if vaping is undermining decades of hard-fought progress against the single largest preventable cause of death globally (responsible for ~30% of cancer deaths) by bringing in new smokers and reducing the urgency to quit among current smokers I can see how public health officials would be cautious about embracing it.