Well they can't really ban bitcoin, so they better try to regulate it, and get some taxes out of it. If they completely ban bitcoin, the only people that will probably stop using it, are those that already follow the law. So in other words, bitcoin would completely move underground, and they would have no control over it. So what's the point in pushing away those that wont give them any problems when they use bitcoin, and make it even harder to catch those that they are trying to stop.