Emile Simpson doesn't think we can just walk away from COIN. As he writes in his book, "Counter-insurgency is likely to remain the more effective operational approach to deal with an enemy who wants to fight in an irregular manner," (p. 11).
"The control of political space is as important, if not more important, than controlling physical space," (p. 6). There is a good master's thesis to be written on just exploring that thought.
And don't think you can just ignore the politics. "One cannot refuse to engage in political activity: the empowerment or marginalising of individuals and groups will occur through coalition actions, whether deliberate or not," (p. 107).
He seems to reject the "hearts and minds" shorthand often used for COIN: "‘Classic' counterinsurgency...was far more about population control than about popular support," (p. 150).
Finally, he observes that classic Western military thought calls for concentration of force against the enemy's center of gravity, but warns that insurgencies generally avoid concentration.
His bottom line: "If in a given conflict the policy choice has been to commit military forces to achieve an outcome in a country in which the enemy refuses conventional battle and lives among the people, counterinsurgency, properly resourced, and in a realistic political context, can be highly effective," (p. 235).
Thomas E. Ricks covered the U.S. military for the Washington Post from 2000 through 2008.