This is all besides the point I was trying to make. It doesn't matter if and how government can stop Bitcoin trades or whatever. It's about what happens when governments simply deem Bitcoins illegal, preventing legitimate use. It will undermine trust, and people will start converting their wealth into something else. In terms of wealth preservation, Bitcoins are just like any other forms of currency, except that there really isn't anything protecting it from becoming worthless.

I don't think there is any kind of currency that survived for more than a few hundred years, there have probably been hundreds if not thousands. Stamps, sticks with carvings on them, silver coins when fiat coins where still actually made of gold (can you believe it?), seashhells, etc. The ones that survived the longest have been government-controlled fiat currencies.

Once again, just to make myself clear, I'm not saying this is a good thing, just making the observation.

You're still thinking very US-centric. So what if US makes it illegal, maybe that kills the US market for it, but there is still the rest of the world. And maybe the rest of the world using it while the US cannot even provides them some advantage over the US (of course this isn't necessary).

On the other hand a 51% attack on the blockchain by _anyone_ would have a near 100% chance of destroying Bitcoin.

Not true, necessarily. There have been proposals to form a "web of trust" for miners, which would prevent this sort of thing from happening.

Miners who have been on the network for longer would have greater authority than new miners, regardless of computational ability. If a 51% attack occurs, it would in effect fork the blockchain, because the WoT-enabled miners would not accept their signed blocks.

You can fork the blockchain now if you want - it's just a matter of getting enough people to agree with you for those coins to have value.

I'm not saying it would be _good_ for Bitcoin - but this is not an insurmountable problem from a tech standpoint.