First, your premise that bitcoin can make Fiat disappear is wrong. What is the reason that you say it so? Banking or Fiat institution has been here and I think they will stay and even though bitcoin has been globally adopted, fiat will not go away. And we should take advantage of both monetary system, Fiat will not be obsolete.
Not all Officials of UN controls a country. As far as I understand, its still the President or a Prime Minister that heads a state and not UN officials. So again your argument is flawed. And no all countries are against bitcoin, do your research and you will see that there's also a lot of nation that is pro bitcoin either by having regulations or adopting it.
And even if a nation ban bitcoin, like China did, their bitcoin community is still thriving, they are still doing trading OTC so it just shows that bitcoin can't be stop.