The Feds' normal procedure was to target a church steeple in the civilian area of Charleston, not any port area. The Feds also shelled Fort Sumter for years and even launched an amphibious attach against the fort, but they couldn't take it. Other forts and Confederate troops outside of the city defended the harbor. Why not attack them rather than the civilians?
Perhaps you'd be interested in Union General Gillmore's demand regarding firing on civilians, which he commenced at 1:30 AM shortly after sending this communique.
HEADQUARTERS DEPARTMENT OF THE SOUTH, Morris Island, S. C., August 21, 1863.
General G. T. BEAUREGARD,
Commanding Confederate Forces, Charleston, S. C.:
GENERAL: I have the honor to demand of you the immediate evacuation of Morris Island and Fort Sumter by the Confederate forces. The present condition of Fort Sumter and the rapid and progressive destruction which it is undergoing from my batteries, seem to render its complete demolition within a few hours a matter of certainty. All my heaviest guns have not yet opened.
Should you refuse compliance with this demand, or should I receive no reply thereto within four hours after it is delivered into the hands of your subordinate at Fort Wagner for transmission, I shall open fire on the city of Charleston from batteries already established within easy and effective range of the heart of the city.
I am, general, very respectfully, your obedient servant,
Q. A. GILLMORE
In other words, give up your forts or I'll kill your civilians. How civilized.
I don't have any totals on Charleston civilian casualties. What I posted came from a couple of books I own and Xerox copies of a few old newspapers.
Well within the terms of the accepted laws of war at the time. Those who don't want their city bombarded are required to declare it an open city, as in WWII the French (and later the Germans) did with Paris, and as America did with Manila.
If you defend it, the entire city becomes, under the laws of war, a fortress. It can be bombarded perfectly legally, as the Germans did with Paris in the Franco-Prussian War and WWI, and as the British/French did with Sebastopol during the Crimean War. Both of these were more or less contemparoneous with our WBTS.
Your beef seems to be with the laws of war at the time, not with the specific Union application of them at Charleston.
Had the Confederacy won at Gettysburg and then moved on Washington, they would have been well within their rights to besiege and bombard the well-defended capitol of the enemy.