I'm not sure what you mean, you ban it exactly the same as you ban copyright infringement or child porn or any of a dozen other crimes that are committed on a computer that simply involve a transfer of information between a few parties.
It would actually be a lot easier to ban than the other things I mentioned since it would require a financial transfer to purchase them to begin with. A better example would be online poker, the ban of real money online poker actually had a pretty big impact on users.
Not sure where you make that assumption from. If bitcoin never gets adopted as legal tender for real world goods its value gets severely limited. If Government's explicitly state that bitcoin is not legal tender, and I can't buy a latte at Starbucks with it then its not very useful.
Bitcoin is already not legal tender. Legal tender means you are _obligated_ to accept it as payment for a debt (eg, in the US, a lender cannot refuse a payment on a debt in dollar bills). It does not _necessarily_ mean that non-legal tenders _cannot_ be used for barter.
I'm not saying that Bitcoin won't have value, my response is to the grandparent that makes the argument that bitcoin usage would explode if it were made illegal. It seems to me bitcoin would be further marginalized in that case, hardly a catalyst for growth.
Forbid businesses from accepting the currency due to stability issues. Also use FUD terms such as "deflationary, the exchange rate changes so much, IRS may take a more active role in investigating sudden influx of cash".
Businesses trying to deal in Bitcoins will find their value going down much faster relative to cash value by end of day. That's the very definition of FUD.