Yeah, the American populace might not care, but the victims do care, and how upset they are made directly affects all other efforts in that area. Peacemaking and nationbuilding only gets more difficult the more people that have lost family members to the invaders.
If we'd gone into Baghdad WWII style, carpet bombing and all that, we'd probably still be fighting a significant war in Iraq. Or the country would be depopulated. Presumably the appearance of ISIS was largely a reaction to western actions in the region, and its initial strength was proportional to the outrage that could be drummed up. Sure, there are probably asinine military commanders that don't account for this, but it isn't the universal rule.
