Unlike Liberty Reserve, Bitcoin's transactions aren't truly invisible. Thanks to the elaborate software architecture that stands behind this cryptocurrency, it's possible to see the web of exchanges involving Bitcoin. But it's not possible to see who is using them, much less what they're buying. Little wonder that bitcoins have a growing criminal constituency, particularly in the unregulated, murky online world of the "Deep Web."
Bitcoin was created to give us freedom and it's online so with freedom online we can do anything we want as long as we have bitcoins, not all people are law abiding citizen because not all laws in this earth are created for the benefit of the majority or the masses.
Lastly, if illegal it does not mean it's wrong.