The reasoning behind the tax is to pay for the anticipated additional health costs associated with tobacco/alcohol/etc. A cynic will obviously argue that the money is just used as general revenue similar to fuel excise.
I did read an interesting article a while ago (can't remember the name sadly) which argued that life time public health costs for smokers and alcoholics were less than the general population, rather than higher. This was based on the lower life expectancy leading to significant savings on publicly funded aged care and pensions. Makes sense if you think about it, as decades of welfare and aged care costs in the 100s of thousands of dollars.
