Why?
Actually, I suspect BOTH cost LESS to taxpayers. Because they don't live as long on average.
All the "studies" on "costs" of smokers and obsese conveniently leave off all the 2 decades+ of social security, medicare, medicaid, food stamps and all the rest that people who live really old cost.
ALSO... the MOST anti-smoking people are ex-smokers. There is limited benefit in quitting along the way - so some. In short, a "smokers tax" should be against ANYONE who ever smoked a cigarette, a cigar or pot in the person's lifetime.
As for obsesity, even being 20 pounds overweight is a known great health risk. Thus, anyone more than 5% over optimum weight (which tends to be very low) also then should pay the "obsesity" tax.
In short, 95% of Americans would just be taxed more. Which, of course, again, is liberal control freakish - for which they alway search for ways to exempt themselves.