A fat tax, while seemingly unjust and moral incorrect on the surface, could actually prove to be beneficial in shaping social ends. It would work as an encouragement for more people to limit their consumption of unhealthy foods, increase their exercise habits, and ultimately achieve a more healthy lifestyle. With a healthy society, the country would run better as a whole and function more smoothly. Additionally, the cost and need for expensive health care would decrease significantly.
Fat tax is not justifiable. Imposing a fat tax is discrimination based on someone's weight. You cannot single out people because of their weight and charge them an additional tax. It is also a violation of privacy because people would have to be weighed to determine if they qualify to the additional tax.
This argument runs along the same lines as eugenics. People have free will and God given rights. Who are you to tell them what to do with their bodies and lives? Taxing an obese person for just existing is beyond heinous. Go ahead tax them, then tax ugly people for being eyesores! What kind of societal cleansing are you advocating for? Maybe we should open "fat camps" and "enroll" people for their own good. Have you learned nothing from history? Let people live the way they want to and live your life the way you want to. I damn anyone who tells me how I should live, think, or speak.