I think its a good idea. I can sin taxes serving multi purposes
1. Raising Revenues
2. Deterring selected behaviors/Social policy
3. Redirecting money
1. For raising revenues, I guess you would compare it to the alternatives to see if it makes policy sense. It is a consumption tax compared to the usually income and property taxes that we are used to paying. As a consumption tax, it does not rely on the principle that it taxes those most able to pay proportionately to their ability to pay like the income tax rests on, but is a regressive tax that targets certain users of products. Is that good or bad? Instinctively I say bad, taxing should tax the rich the most and the poor the least, here everybody pays the same tax regardless of income. However, another function the government is to deter behavior that is associated with externalities and is inefficient, which leads into
2. Deterring selected behaviors. Smoking not only cause lung cancer, where the government has to pick up a large piece of the tab, but also second hand smoke costs non-smokers and their insurance company lots of money (another externalities). Whereas the the government cannot give money to people who develop cancer cause of second hand smoke they can make the users of the product that cause externalities pay for as much as the externalities as administratively possible. Same goes for alcohol and drugs. Alcoholism often leads to homelessness, inefficiency at the work place, breaking up of families, drunk driving accidents. Like cigs, alcohol is addictive and thus criminal penalties will only have a limited effect, the best way to deal with this behavior is to deter it before it starts or make the users pay for as much of the externalities as administratively possible. Criminal laws don't compensate families of drunk driving victims nor children affected by their parents divorce due to alcohol, sin taxes can at least somewhat help allievate the externalities by deterring the activity in the first place and paying for some of the costs associated with the externalities.
3. A consumption taxes taxes consumption of certain activities leading to money being spent elsewhere. Such money might be invested or might be consumed in other activities, but if money is more productive being invested or being put into another activity then its good economic policy to redirect the money.
One last point, 2 and 3 were used in justifying one, but sometimes consumption taxes are needed because they are the only feasible way of raising revenue even if in a perfect world, income taxes could be raised to make up what the consumption tax brings in. You might have a scenario where have through policy analysis you rank three alternatives in this order 1. Raise income tax .5%, 2. Sin tax, 3. More debt. In that scenario even though points 2 and 3 would be validly in assessing the options of the incrase income taxes and the alternative sin tax, if an increase in income tax is not politically feasible, then you can disregard my second and third points and still advocate the imposition of a consumption tax.