If a government decides to make trading or possessing Bitcoins illegal, questions will be raised about how exactly it will enforce such a ban. It is impossible for a government to seize your Bitcoins, unless you decide to handover your private keys. However, the majority of citizens and institutions like to stay on the right side of the law. So the demand for Bitcoin would plummet if the government decided to ban it. All exchanges in that country would also be shuttered and buying/selling Bitcoin would be difficult and risky. This would suffocate Bitcoin in that country and the government’s objectives might be achieved.