I believe that a land invasion would be a disaster. We should content ourselves to arming opposition groups and to dismantling Afghanistan via a vicious air war.
Until the supply lines are secure, whether through Pakistan, Uzbek, or Iran, ground invasion is out of the question. Which of those supply areas is secure that you would turn your armies loose in Afghan?
I agree. The terrain is vicious! I actually felt sorry for the Russians at having to endure it and withdraw. The Afghans have centuries worth experience in fighting in this environment just as a matter of course ... and they don't wear shoes while doing it! Argh.