If a 51% attack is launched, and a government gets enough control of the currency to dictate where it goes, how much transactions cost, and how much of the currency is created, then how will Bitcoin be any different from the current central bank controlled fiat currency system? I think a government with your goals would be way more effective if it just slapped a unique id on every dollar, and tracked all the transactions from the central ledger it already has. End result will be the same, and it won't cost a ton in mining gear. Especially since the ONLY purpose of mining is to secure the system in a DISTRIBUTED manner. If the ledger is already centralized, there is no need for mining.

Though, I suspect the people would be a bit upset if they found out their government is planning on tracking every single dollar they spend. In much the same way Bitcoin users will be upset if they found out some entity is trying to gain 51% mining power. Also, you are still misunderstanding how Bitcoin works. 51% doesn't give you the control you claim it does. At most, the 51% holding government will be burning a ton of energy while rejecting almost all transactions and transaction fees and creating orphaned blocks, while the remaining pools will continue earning fees and creating blocks the general population would agree to be valid.