Sin taxes cover a wide range of social activities, some legal, and some not. Those that are not legal include the use of certain drugs such as marijuana, or on deadly weapons such as switchblades, and even some types of fireworks such as M-80's.
We The People want our basic human rights and civil liberties to be protected under the law! We want to be able to protect ourselves while still gaining pleasure from having powerful weapons! We want to be able to sit back and relax when we are restless or can't relax on our own by using our drug of choice. We just want to be ourselves without prosecution, as we would rather pay our taxes than being treated as criminals!
Time has proven over and over again that the government is biased by being selective over what's legal and what's not.