As earthmama suggested, I think it's the act of smoking itself as much as the nicotine that provides a calming effect.

But smoking is also dangerously unhealthy, and ridiculously expensive. Of course people are always free to make up their minds about what they want to do. But I wouldn't start a habit up if it could be avoided.

This coming from the coffee-addict, of course. But at least coffee is much cheaper, and in reasonable amounts is actually shown to be quite beneficial to one's well-being.