Bullshit.
Be weary you pesimists and pacifists, here goes my counterpoints.
You can win a war in Afghanistan. Hills and mountains don't fight, people do. People, the Taliban in particular are the problem. The terrain aids in the problem, but it isn't everything. Three historical examples of how history's underdogs have won wars.
The earliest example of people doubting the ability of a force to destroy another, is actually a converse of our present situation. The American militia, after YEARS of intense fighting in the colonies, defeates the greatest power since Rome, Great Britian. We were the first sucessful military rebellion against the crown, if Washington had listened to the nay-sayers there would be no United States of America.
The second example is little known, but important. The Russo-Japanesse War occured in the late 1800s, and for the first time in century's a European power was defeated by a Asian power. The Japanesse won the war against one of the most formidible empires in Eurasia, Imperial Russia under the Czars.
The third, which was stated earlier is the United States again. For nearly two and a half years of fighting in WWII, the Nazis stormed across Europe, into Asia, and Africa. The mighty French were defeated, the British back on their island, contemplating a peace treaty, and the Soviets on the defensive. America invades North Africa w/the Brits and we get our ass reamed by Rommel at the start. After years of fighting, Rommel leaves Africa, the Soviets push the Nazis back from the gates of Moscow, and Stalingrad, and finally in 1944 the second front on Europe is opened at Normandy, France.
What if Roosevelts people said that the a war against the Nazis couldn't be won? The United States would speaking Germany and Japanesse, or at least every European would be wearing Swastikas.
We have no choice but to fight.
If anyone want's to dispute this go ahead, I'm ready to back up my statement.