So let's say the powers that be (IMF, WorldBank whoever want to kill off Bitcoin it seems to me a lot easier to do than one might think.
All that has to be done is to purchase and hold all the bitcoin as they become available, no mass buys, just quietly over a period of a few months or even years ( Currently over 1.5 Billion Euro (May Friday 26th €1,623,482,367) is traded daily so in a short time you would have acquired the majority of all coins being traded.
Prices may go and up and up but as they have all the money in the world (They own the printing press) and as the coins become more and more expensive this will free up more and more of the coins being held and eventually the majority of coins are out of circulation to a point where there are so few Bitcoins that they do not worry about them and it's game over- Thank You for playing.
I have heard other people comment on ways governments can kill it
They can make it illegal or impose a 50% tax on all bitcoin transactions. make all transactions reportable to the IRS, etc etc.
Most transactions are done on exchanges so are already reported to IRS, Kraken Coinbase etc,
Other cryptos will take over from bitcoin if the government bought it all.
They have endless money, they own the printing press or maybe an outright ban on creating, owning or trading any competing currency with the national currency of the country.
The one WORLD Currency is already in train. It will be issued by the IMF it will be totally digital and totally controlled. It will be subject to 2-3% inflation so your currency will dwindle to nothing even if never touched.