If we take the view that Trans fat is poisonous, how would it be different than regulating the use of lead pipes for water supply?
First, you'd have to prove that trans fats are poisonous. Since that's not possible the rest is meaningless. Unless you want to begin banning all sorts of foods that could be bad for you if you rely on them for too much of your total caloric intake. Personally, I don't like others telling me what's good for me when it comes to food (and many other things) because I find they don't have any idea what they're talking about and are nothing more than control freak busybodies.