Should We Have a Fat Tax?

Dave at the Crisper has an interesting post on the possibility of taxing those with a high BMI (Body Mass Index). Should we also consider a tax on crappy genetics or how about just plain bad luck? Because hey, my BMI is 20 and I'm not doing so good in the health department. Could it just be that some people find fat people offensive? I wonder how far the food Nazis are willing to go so that they do not have to bear the unsightliness of the overweight?