There are always trade-offs. From the British Medical Journal in June:
We think these results have important implications. They show that overweight and obesity were already common among women who had never smoked in this population more than 35 years ago, its true extent concealed by the high smoking rates in the population as a whole. They suggest the decline in smoking rates in recent decades may have contributed to the increase in overweight and obesity. Although lifelong smoking is clearly responsible for much higher mortality rates, obesity, and especially severe obesity, is an important contributor to premature mortality.
To what extent is smoking used by low-status women to stay thin? Beyond the health question, it would be interesting to explore some other trade-offs. Does smoking or obesity have the greater effect on fertility - both in terms of likelihood of attracting a partner and the physiological effects? And what of satisfaction with or quality of life?
While the authors are clear that smoking is a larger contributor to mortality than obesity, studies like this are a sound reminder that policy decisions are full of trade-offs and unintended consequences.