they would easily be able to do that,

it costs just 6 billion to destroy bitcoin with a 51% attack

this is something a commited developed country easily could affort,

however the developed countries promote and support cryptocurrency as cryptocurrencies are benefiting them more than the developing countries, so there is a division in the united nations consil, which prevents state sponsored 51% attacking as being legal.

however if there is an intelligent bussinesman who lends a ton of money to create this hashpower as some form of cyberweapon of a state, this could truly exist.

and what makes it worse this cyber weapon would then be able to eat more and more as each destroyed cryptocurrency would make the attacker even richer, which he can invest to have even more hashpower

regards