First, fois gras wasn't banned as a health issue, it was banned due to animal cruelty. Some people objected to the forced obscene overfeeding of geese in order to create especially large, fatty livers. A small confession. I've eaten fois gras.

Regarding the banning of trans fat cooking fats at restaurants. First, they never bothered to tax it, they just banned it. So there's no connection between taxing and banning established by that example. Second, if you personally want to you're more than free to go out, purchase a container of trans fat cooking oil and down it at your leisure, even in Chicago. Last, you're resorting to the slippery slope fallacy again. There is a reasonable case to be made for banning trans fats in restaurants and a reasonable case to be made for allowing their use. Whether to ban or not to ban should be made on those merits. There's nothing in Chicago's ban that suggests that donuts, cakes, chicken wings, and twinkies will become casualties.

Here's your slippery slope in a nutshell, I'm trying not to put words in your mouth:

Chicago banned trans fats in restaurants. We're going to end up with government controlled health care. The government is then going to do all sorts of onerous things you don't list regarding smoking, alcohol, and unhealthy foods.

--We aren't anywhere near getting government controlled health care. At best, we'll end up with a public option, not a single payer system with doctors, nurses, etc all employed by the federal government. Simply because Chicago banned trans fats, does not mean the government will move legally against unhealthy habits. If there's a public option, they would probably adjust premiuns if possible, but health insurance companies already do this. Why would a government insurace plan behave any differently.

It's also possible to construct a leftist slippery slope out of the Chicago ban.

If we don't ban trans fats, then eventually restaurants will eventually be cooking with even cheaper, more questionable chemicals, maybe even toxic byproducts from chemical plants.