David French at NRO spells out the five reasons:The counter-arguments are too familiar: It’s no business of ours what happens in places like Iraq, Syria, and Afghanistan. Small improvements in the security conditions of lawless countries aren’t worth the cost in American blood and treasure.Those who believe such things also have to believe that the U.S. did the right thing in staying out of Afghanistan for years after the Soviets were driven out and the Taliban offered up the country as an operations base for al-Qaeda. They must think that President Obama was wise to withdraw troops from Iraq in 2011 and allow jihadists to reconstitute as ISIS. They’ll presumably stay mute if al-Qaeda, ISIS, or some other group launches an attack on America that’s been planned in one of the countries from which we’re now withdrawing. And surely they’ll not be concerned when the next wave of fleeing refugees hits the West.
Third, while it is difficult to predict any given terrorist attack, this much we can say — when terrorists obtain safe havens, they become dramatically more dangerous. The creation of a safe haven escalates the threat and renders serious attacks a near-inevitability.
Fourth, for reasons too obvious to outline, terrorist safe havens are always in nations and locations that are either hostile to the United States or in a state of fractured chaos. Terrorist may operate in places like France, but a true safe haven cannot thrive in functioning, strong allied territory.
Finally — and this is critically important — the national obligation of self-defense is permanent. No functioning government that abdicates its duty to protect its citizens from hostile attack can remain legitimate. Preferably self-defense is maintained by deterrence. But when deterrence fails, a failure to engage the enemy doesn’t bring peace, it enables the enemy to kill your people.Michael Ledeen at PJ Media offers the wider perspective:
How often have you heard warnings that the withdrawal from Syria and Afghanistan will make war more likely? They don’t seem to realize that the war is on, right here and now. Nor do they see that it’s a global war, and that we face a coalition of radical Islamist and radical Leftist regimes, from China and North Korea and Cuba to Russia, Iran, Turkey and Venezuela. Our enemies, who fear and despise freedom, are well aware that this is a big war.That's why signals such as all this withdrawal talk will have consequences.