You have to think of it more as peace keeping and yes it it’s a sunk cost. But would you rather have to send thousands of more troops in a few years to reclaim land when Iraq’s non-existent military gets destroyed by guys in Toyota Trucks.
Fight them there or fight them everywhere because it’s only so long before they’re setting up training camps to go global. Keeping ground forces their helps to keep disorganization.
And it’s only going to get worse. We may not see it in our lifetimes, but how do you think this region will do when oil isn’t the be all end all? Water is already scarce in the arid regions, the world’s heating up, it will be even harder to come by. Corrupt religious governments, warlords, less economic chance for success, and less water. This area will be a thorn in our side forever.