>Easy - I collect taxes at the point where physical goods are exchanged for bitcoins or are used to deliver products.
Or just collect the taxes at the point where it's converted from BTC to a real, government-backed currency. It's simpler, because there needs to be a paper trail there.
> The state does this, but people already get around this by conducting cash transactions. Bitcoin creates another option for this.
Govts tolerate a certain amount of black market because it costs too much to reduce the black market to 0. However, that toleration goes away when govts are seriously hurting for revenue.
Easy - I collect taxes at the point where physical goods are exchanged for bitcoins or are used to deliver products.
If you can't use bitcoins for food, housing, netaccess, or energy....