Fieldthistle,
This article should answer most of your questions:
http://en.wikipedia.org/wiki/Trans_fat In general, the type of Trans Fats that are most common in our day-to-day diets are hydrogenated and partially hydrogenated oils. Several years ago, McDonalds stopped frying their fries in Beef Tallow and replaced their oil with Hydrogenated Oils, ironically making them less healthy.
Essentially, trans fats raise bad cholestrol levels in your blood (LDL - high amounts of this is linked with heart disease) while simultaneously decreasing good cholesterol levels (HDL - this can remove LDLs and transport them to the liver where they don't harm the heart), the only types of fats that acutally do this.
The benefit of using these oils is mostly one of cost and that they help food products to be preserved longer and have a longer shelf life. Which is why the main opponents to banning them will be businesses. Even then, hard to say if it will be more expensive.
Although in that Wikipedia article, KFC says they have to stick with Trans Fats for matters of taste, my guess is that's BS and largely porofit-driven - real oils taste better anyway - Trans fat is invisible, odorless and tasteless. Same with some McDondald's reps talking about how in European chains of McDo, they use different oils for their fries dues to "cultural taste differences." Again, more BS. The process to change oils would cost Ronald McDonald a pretty penny.
Removing trans fats will not eliminate fried foods, nor will it make those foods taste worse.
