Trans-fat is extremely unhealthy for humans to consume. It is also essentially invisible in terms of flavor or appearance. Since it is so difficult to see/taste, it is better that the fat be banned. Further, there is absolutely no reason for trans-fat to put into foods, but food companies do so to save money.
The banning of trans fat is a health issue, obviously, but it is also an issue of general product safety. The government not only has the right to protect consumers from corporate greed, it has an obligation to do so. Nearly all consumer products are regulated before the government will allow them to be sold to consumers. If they are not safe, they cannot be sold. Trans fat and products containing trans fat should be no different.