People have to take responsibility for themselves.
that's cool, but then it has to go all the way - if you're responsible for making good food choices and exercising and what not, but you fail to do so then you've also got to be responsible for the burden that places on society as a whole when you get older and spend many years in poor health. this is currently not the case and to be totally honest, it would be a pretty horrible way of dealing with the situation. i don't want old, sick people being turned away from medical care or burdened with massive debt because they aren't covered by medicare or are too poor for insurance - that's not the Australia that i want to live in.
how do you determine whether you're treating someone who has done all the right things but is genetically pre-disposed to certain "lifestyle" diseases, or someone who lives on a steady diet of sugar and has never bothered to exercise in their lives? sorry for the straw-man, but when you follow the idea through to its logical conclusion then there's millions of reasons as to why it doesn't work.
also, the whole "personal responsibility" thing irks me - it makes a massive assumption that people are smart enough to figure out what to eat and how to make good food choices. simply put, a lot of people are just not equipped for this. i really care about this stuff and i try really hard and it's still taken me the better part of 30 years to find a dietary combination that actually works. what chance do you give the average person?
i don't really see "personal responsibility" as any sort of solution - that's what got us into this mess in the first place.
i'm pretty neutral on the topic - i think a "fat tax" would be an extremely broad and general stroke to attempt to solve the problem. it's definitely far from perfect and it's not exactly going to stop the fatties in their tracks, but if it does anything to help counter poor food choices, to help fund the treatment of lifestyle diseases, to help fund education for children and teens and to subsidise certain "healthy" and/or "fresh" foods then i think it's a better option than just saying "personal responsibility, nanny state, ra-ra-ra". yes, people who are healthy would be paying into the fund everytime they sneak maccas or a chocolate bar, but it's the price you pay to live in a society such as ours - i pay for roads i will never drive on, trains i will never ride, hospitals i will never visit and services i will never require but that's just the way it is.
wrt what a "fat tax" would actually entail, i dunno, but surely a combination of energy density, sugar content and some level of "processing" or "denaturing" could be used to determine a list of less desirable, taxable foods.
this is all moot though, cos it will never actually happen...