The government is trying to banish trans-fats from food, why ar they so bad for u?

Heart disease. Meats have some transfats, but most are manmade. Transfats are made by hydrogenating oils, which turns them into solids (shortening). Transfats are used in processed foods b/c they last longer on shelf that way -- cookies/pie crusts/chips/popcorn/donuts/creamer/margarine. They raise LDL (bad) and lower HDL (good) cholesterol, which leads to heart disease. Saturated fats are just as bad!
Foreign Biochemistry. All our genes/enzymes which process fats are designed for cis-fats. "cis-fat vs. Trans-fat" refers to the carbon-carbon spatial bond pattern when double bonds between adjacent carbon atoms, are converted to single; lookup in google images. All living cells break double bonds to cis-bonds. Trans-bonds create processing problems for our genes/enzymes which are not adapted to properly handle these.
Cause many illnesses. Most trans fats come from partially hydrogenated oils found in many processed & fried foods like french fries & donuts. Simply put, trans fats are highly toxic.They cause inflammation, raise cholesterol & may cause up to 100, 000 deaths in the us from heart disease each year. They also increase risk of alzheimer's disease, diabetes, obesity, depression & infertility. See my comment for some links.