Double-Duty

While I hate the use of the term "The Mission" in the context of our presence in Afghanistan (to the extent of sometimes putting a "tm" beside it), it's been effectively sold as just such a thing.
A "missionary" activity, bringing the benefits of Western liberalism to the starving and oppressed people of Afghanistan.

We're not at "war" with the Taliban. We're supposedly suppressing a medieval insurgency while assisting the elected government of President Karzai, in his heroic attempts to modernize and democratize his backward land.

Truth be told, I don't think that even the elites see Afghanistan as all that strategically important at a geo-political level. That's why bush II has generally neglected it.
Iraq and Afghanistan help to surround Iran, and project power out towards Russia, Pakistan, and China as well, but I don't think it's crucial to pacify the country, just prop-up a government that permits airbases.

Canada got into this to curry favour with the USians, and now, as was pointed out recently on Znet.org a lot of Canadian defence contractors have seen the lucrative possibilities of a war without end.

It's certainly red meat for the slavering morons who gravitate towards the Conservative Party.