Answer:
Three little letters. A paradox to some. The worse that it is, the better it becomes.
Give it food and it will live, give it water and it will die.
As soft as silk, as white as milk, as bitter as gall, a thick green wall, and a green coat covers me all.
Though not a plant, has leaves. Though not a beast, has spine. Though many wouldn't need this thing, It's more valuable than wine.
What is that over the head and under the hat?
They are many and one, they wave and they drum, Used to cover a state, they go with you everywhere.