Sugar tax is not there to bring the usage down but to rape more citizens. Sugar can be addictive and used in allot of products, so it is just an easy way for government to get more pocket money and to make citizens spend more. Will the price of sigarettes make a smoker stop smoking, no. They call it "sin tax" because it makes the corrupt government sin and the citizens pay the price.
Not if you consider that coke only affects the person who drinks it. Smoking stinks, a majority of smokers (not all) couldn't care less about the People around them and it affects not only the smoker but all have to inhale the stink rubbish.