They ban it because they can't control it. Governments are in the Control business.
That is true, the government wants to be the one controlling their people but with bitcoins we can have a freedom because they are decentralized so no government can be involve which means there are no taxes to be made. That is why some government thinks that the bitcoins i s a threat into them because it can be a start of a rebellion for some of theur perspective because people can now have a freedom in currency so whats next is freedom into everything. But if they just team up wuth this thing it cannot be a threat at all.