"The British failure in Basra was not due to the conduct of British troops, which was exemplary. It was, rather, a failure by senior British civilian and military leaders to understand the political dynamics ... in Iraq, compounded by arrogance that led to an unwillingness to learn and adapt, along with increasing reluctance to risk blood and treasure to conduct effective counter-insurgency warfare...
...British commanders attempted to cut deals with local Shia leaders to maintain the peace in southern Iraq, an accommodation that was doomed to failure since the British negotiated from a position of weakness."
To my mind, the key line in this critique is the last one. Governments should only talk to terrorists and insurgents when it is clear that the terrorists or the insurgents are losing militarily. Talking from a position of weakness simply emboldens them, encouraging them to think that they are on the verge of success. This is why it would be so foolish to reach out to the Taliban now.
Hat-tip: Tom Ricks