I do agree that the US Government will shut down bitcoin fairly soon, for the same reasons it doesn't allow people to create any other kind of currency.
I consider governments to essentially be criminal gangs that have achieved enough power to be able to buy legitimacy. Money laundering allows 3rd party gangs to start to claim legitimacy too, so it must be stopped. This is not to discount the good things governments (and gangs) accomplish, just to call attention to the good and bad done by both. Governments generally have elaborate propaganda and disinformation arms as well, and use money laundering laws to attack the funding channels used by competitors (described derogatorily as gangs).
How about an assassination market? Especially as far as present governments are concerned, this would be an enormous downside to the existence of an anonymous payment system.
Disclaimer: I am not declaring that assassination markets would necessarily be bad for humanity (I haven't thought about it enough), but on the surface it's definitely something that most people would consider to be a potential "bad" outcome of any anonymous payment system.