Had Lincoln chosen a measured response, such as sending a contingent of marines to invade and recapture the island on which Sumter was located or even to occupy Charleston's harbor area, I doubt you would have gotten the same response.
Substantial areas of the south (what is now West Virginia and populations on both sides of the Appalachians, especially eastern Tennessee) didn't ever warm to the Confederacy, or did so only late in the conflict in reaction to the Union Army's deprivations.
The first major shooting battle of the war was a direct reaction to the Union Army's invasion of Virginia.
It was ordered by the confederate government in Montgomery, not by the South Carolina government.
Had Lincoln chosen a measured response, such as sending a contingent of marines to invade and recapture the island on which Sumter was located or even to occupy Charleston's harbor area, I doubt you would have gotten the same response.
So let's see. Ft. Sumter is in a harbor, surrounded by enemy batteries that have just forced it to surrender. And your plan is to chug some boats into that harbor, under the enemy guns, land some marines and then what? Wait for them to be shelled into submission, too?