I would be more concerned about a Microsoft or Apple attack on Bitcoin than the Government. Government will attack by regulation, but big companies will attack with dollars.
Just in your wildest dreams, imagine that the Bitcoin Foundation becomes disfunctional, slow to innovate and doesn't respond to serious problems discovered in the protocol. I know, that could never happen, but just play along with me here.
Microsoft senses an opportunity, so they step in with a new BTC client that is now going to be embedded on all Windows computers virtually overnight through a point update (Windows 8.2 we'll call it). It's "on" by default, and quickly surpasses 51% of the nodes on the network. MS even hosts the blockchain on their cloud drive so you don't have to download the entire freakin' thing to your computer/device.
They fork btc, centralize the block chain, honoring all bitcoin that happened before the fork (except Satoshi's known stash and some known stolen bitcoin, which gets them good press as they claim to squeeze the criminals out of Bitcoin). Simultaneously they do a couple of strategic acquisitions to tilt the ecosystem in their direction (buy Bittrex and/or Cryptsy, a few large miners, a bank).
Merchants and other miners flock to "MS Bitcoin" because now it's backed by a huge company that has relationships with other huge companies and seen as safe while still laying a claim to the Bitcoin name. The old fork drifts off into oblivion with us hardcore "stand your ground" libertarians and the BTC Foundation, while MS implements POS and other ungodly things that the masses don't care about; all they know is that it just works and it's kinda cool and it's supported by safe ol' Microsoft instead of crazy nerds who talk in a funny technical language and argue all the time. Bitcoin Girl is hired as spokesperson. Wall Street and most VC's cheer as MS announces a "MS Bitcoin fund for start ups." Eventually it's rebranded as "Bitcoin Dot Net" and then just "Dot Net" as it's embedded into Visual Studios as a payment app.
It would hardly take a few billion dollars, chump change to these guys.
They would not be able to profit off of this. Regulators would also not be happy about this and would make MSFT pay (a lot - billions, maybe tens of billions) for doing this.
A couple of years ago, a gaming company, by default had gamers' computer mine bitcoin while they were playing their game on their computer (back when CPU/GPU mining was still economical). The company ended up making only a few hundred bitcoin (I think, but this is also when BTC was trading at much lower levels), but were fined several million dollars (for a few thousand dollar profit)