In a supposedly free country? No, of course we shouldn't ban it.
Mandate that any product containing trans fat be labeled as such, and with appropriate health warnings (like they do on tobacco products), but outright bans of things we can only use to harm ourselves is anathema to liberty.
Why do people flip out about these basic tenets of modern civilization? Sorry, most people don't want poison to be sold as food. Go ahead and sell transfats all you want, but don't tell people it's food when it is most certainly not food.
At this point, transfats seem to be harmful food adulterants. Food companies are already banned from putting terrible shit into our food. If you're calling it food, it better be composed primarily of food, not poison. This is not some huge encroachment on the liberty of Americans.
How about we go ahead and ban the transfats (like other things that seem like they might be poison) from the general food supply so nobody accidentally eats it, and then everyone who wants to eat the stuff can get some and put it into their food themselves. I feel this latter group would be a significant minority of the population.
Similar to rat poison, which food producers are not allowed to include in food, but you can buy from the store yourself and put into your own food if you like. This is comparable to the current situation with tobacco products.