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.
Unless consent is forced.
Foreign intervention abroad is not in our constitution. Thus I don't consent voluntarily to supporting such a war effort.
And by the way, altruism is a fraud. I'm surprised that you seek to legitimize it. Even Rand doesn't do that.