There is obviously a huge risk in sending an extra 40,000 machine-gun wielding troops into a country they don't understand to "clear" huge areas of insurgent fighters who look exactly like the civilian population, and establish "control" of places that have never been controlled by a central government at any point in their history.
To justify these risks, the proponents of the escalation need highly persuasive arguments to show how their strategy slashed other risks so dramatically that it outweighed these dangers. It's not inconceivable – but I found that in fact the case they give for escalating the war, or for continuing the occupation, is based on three premises that turn to Afghan dust on inspection.