"Civilians" who support a murderous regime during wartime are fair targets. This is how lessons are learned. Although I agree that it might have cost more Allied lives up front, the peace that was won has lasted generations.
I don't hear any Japanese or Germans screaming "Death to America!" (except for their wacko left. Same as here). In fact, just the opposite. Both of those countries have been blasted into extreme pacifism.
Tikrit, and any other Sunni cesspool should be flattened. If the attacks continue, keep flattening. Muslims understand savage, brute force even more than the Germans or the Japanese.