Only the decision to delegate matters on national interest to the government needs to be made by the electorate. Each particular decision need not be decided by plebiscite. Even then, 100% is not required. When a government works inside its constitutional perimeter, it does not need to check back for 100% approval. There is much to be argued here theoretically , but not on this thread which is about concrete issue of foregin policy. The notion of universal consent was argued for example, in
(Pursuit of Liberty). No Treason. The Constitution of No Authority. Parts I-II.
(Pursuit of Liberty). No Treason. The Constitution of No Authority. Parts III - VII
(Pursuit of Liberty). No Treason. The Constitution of No Authority. Parts VIII - XIV
(Pursuit of Liberty). No Treason. The Constitution of No Authority. Parts XV - APPENDIX
Not every war with a petty dictatorship serves the national interest. Some do and some don't. What is argued here is that a war on the Arab dictatorships and monarchies that nationalized our oil in the 50's would have been in the national interest, because it would have maintained our economic independence, -- a pretty clear cut case.
I agree with the implications that you make, that after we crush the dictator we can't just leave. In Defense of Liberty: The Contours of Victory I argue for the restoration of the principles of imperialism, and for reopening the lessons of colonialism. Since our security lies in distant lands, we must learn how to subdue and manage these lands.
War on foreign soil and used with taxpayer money allows for no withdrawal of support for that war by its citizens. Thus it is immoral even if the goals are supposedly just as it forces those who do not agree with those goals to support them by force.
And that is as anti-libertarian as it gets. By the way, Objectivism is not the same thing as libertarianism. The fact that Rand can justify the use of force on foreign soil (if she even does in the article you posted) puts her at odds with libertarian principles.