1. Will the government of a country ever want their banking sector to be abolished?
2. How will the government collect taxes from the people?
3. If the government can't keep track of people's legitimate money, won't corruption increase?
1. There will be less possibilities for all 100% of one country's people are going to adopt bitcoins so that their central bank to be abolished. It might take decades of time for each and everyone to adopt bitcoin because bitcoin is highly technical one which may not be suitable for old agers and illiterate.
2. Only taxation based on how much you're earning might not be possible but there will be no problem on collecting taxes on buying and selling services and goods.
3. Corruption or money laundering or tax evasion are not new things just because of bitcoin payment system. Government must improve themselves to catch such incidents.