I am not a Libertarian but I have seen enough to have a guess.
In the event of a major crisis the need to keep some people from harming other citizens would neccessitate some of the actions you listed above. And if the need to protect people from other people does not exist then those government actions are not needed.
Let's talk about that list:
forced quarantines - this might be needed as sick people are a hazard to the healthy.
the introduction of military police - this might be needed to accomplish the first.
the restriction of movement - this might be needed to keep the disease from spreading too rapidly from sick who are a hazard.
the complete regulation of commerce and commercial transactions - I have visited sites like fluwiki and the government sites too and have not heard anyone talking about the need for this.
the seizure of vital infrastructure - same as above.
These last two things should really make us all feel uncormfortable Libertarian or not. Even the first few are uncomfortable but at least there could be justification.
I would think that government control or heavy regulation of the distribution of goods and services would occur in any massive crisis, even during an influenza pandemic. Markets would pretty much grind to a halt with government being forced to insure the survival of the nation's accumulated wealth through protection measures. For example the seizure private food, health and other supplies would occur in varying degrees to address the needs of the populace within the context of societal breakdown. It also might be prudent to seize certain services operated by private companies through public infrastructure to insure their stability and maintenance
But an Influenza pandemic is just an example of such terrible or sudden hypothetical crises and isn't the exact focus of my post.
Libertarianism seems to be flawed on the basis that is it ideological, inflexible and uncompromising. Thus it cannot react to hypothetical crises or constant inconsistences and complications within society. If libertarians concede that their ideology cannot successfully address these hypothetical occurrences it leads reasonable individuals to conclude that the ideology itself is fundamentally flawed. If libertarians can ignore their own ideological principals when they view it to be prudent, the rest of us can ignore libertarian principals whenever we believe it to be prudent as well.
What is harm? What are rights? How do we react to political and other circumstances? Blah subjectivity!
Fortunately most of us have significantly more expanded social, economic and political concerns than ideological libertarians. Uncompromising ideological tomfoolery just doesn’t make much sense. Flexibility, reason and the rejection of ideological and rigid thinking seems logical.
Hence we have no qualms with measures and certain responses to dangerous crises.
