What if there were a terror attack like 9/11 financed with cryptocurrency or the US government decided that the risks to financial surveillance and tax collection posed by cryptocurrency was so high that it decided to launch a war against cryptocurrency like its war against drugs or radical Islam and was willing to spend upwards of a trillion dollars over the next several years to combat it? Couldnt they just mount 51% attacks on every current and future cryptocurrency and freeze all transactions?
This is not an unlikely possibility, especially as a result of a nuclear explosion or a new world war.
Goverments would institute new laws that no citizen is allowed to use/sell/trade/hold cryptocurrency
and doing such would be the crime itself (Likely related to terrorism or helping the enemy state weaken
your country's financial war machine). There will be no direct attacks on the network itself such as
with DOSing or 51% attacks, they will just outlaw Bitcoin outright and send people to jail for 15 or
more years if caught. That alone will cause cryptocurrencies to almost fully diminish and if still
survives, go far underground. The only need for government to spend money will then be to
locate miners, developers, and node operators and imprison them.
It is important to remember that Bitcoin only exists now because of the Western understanding
of human rights and how certain tech can help bring in new "enlightenments" to accompany and
add to those rights. In times of oppression or outright world devastation, all such ideals fall to the
way side to help win the war or whatever.
I think Bitcoin can survive such times, but it needs certain changes that helps obfuscate many aspects.