It CAN be taken away from you. Any government can shut down the internet. Try trading BC without it. Try crossing that border you mentioned.
Governments can also make it illegal. You can trade it just as easily as you can buy and sell any illegal drug then. Of course the only people willing to do that will be other people doing something illegal, curbing your markets sharply.
The US government can create their own virtual currency. Your BC will be instantly worthless.
BC IS a dangerous Ponzi scheme.