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.
Altruism is no vice. According to Rand, intervention is justified whenever the invaded nation has no basic freedoms. If it is done for atruistic reasons, the national interest is not served, but the intervention itself is still rightful. Intervention for oil, or in retaliation for the Twin Tower massacre whould clearly serve the national interest, so that point is moot.
The issue of consent as you raise it, is also misplaced. Consent for basic constitutional function of the government is presumed in the very existence of the government. Then, majoritarian consent for specific policies is sought periodically at election time. It is when the government violates your rights by stepping outside of its constitutional perimeter that universal consent becomes a necessity.
Whatever the differences between libertarianism and objectivism -- and I am aware of them, -- a quote from Rand surely qualifies as a libertarian source. For some reason the libertarians today deviate from their own orthodoxy, and the Libertarian Party has foreign non-intervention on its platform. Funny how this abandonment of libertarian principles in search of a pacifist vote did not propel LP anywhere.