Note: when I say "ban", I mean pass legislation or use some other means to effectively prohibit Bitcoin usage, purchase or other acquisition.

Let's take Fincen, for example. The heads of Fincen are clearly aware of Bitcoin and probably understand it entirely. With that in mind, they undoubtedly see its potential and I'd bet that they all own some (as most people who understand Bitcoin do). For that reason, it is in their financial best interest not to ban it.

Morally, you would have a very tough time convincing yourself the potential for bad outweighs the potential for good with Bitcoin and so it is in their moral best interest not to ban it.

Both of these reasons also make bribery or other corrupted means by those who are threatened by Bitcoin far less effective.

This applies to everyone in a position to write anti-Bitcoin legislation.

Short of a "ban", a superior currency will inevitably prevail.