Thats not really using logic. Guadalcanal was winnable, all you have to do is remove Japanise resistance from the island. The current war, the "lets get rid of world terrorism" war cannot be won. Therefore there is no point in fighting.
At the time of Guadacanal remember that we (the Allies) thought we'd have to invade Japan and kill just about every man, woman, and child on the island. Remember, these folks were fanatical. Winning in Japan seemend just as remote as winning against terror sounds, though perhaps more neatly packaged.
However I don't understand the argument "we shouldn't even fight". Okay, perhaps we shouldn't fight in Iraq, maybe that particular conflict was poorly chosen (not that I believe it, but I'm not arguing that point). But "not fighting" against terror means either we accept terror attacks, or give in to whatever the terrorists want (not possible since many demands conflict), or bury our heads in the sand and ignore the world. Do we stop gathering inteligence on terrorists? Do we stop breaking down appartment doors, disrupting terrorist cells, and arresting terrorists? Do we un-freeze the frozen financial assetts linked to terrorists? Or should we only do those things because the loss of life of these activities is small. If that's the case then is it merely the calculus of body counts that makes the fight against terror unpalitable? If that's the case then how much is freedom worth in terms of bodies? I'm not talking about Iraq, I'm talking about doing anything risky to fight terror (sending people under cover to gather intelegence is risky, paying locals for information puts them at risk, etc). Exactly how low is your risk tollerance?
Or are your comments purely about Iraq? If they are then that's not the war on terror (despite claims by the politicians).