But you must look at that event in the fuller context. The South could not have just sat back and let the North “resupply” forts or areas that no longer belonged to the North because if they just sat back and let the North occupy Dixie... they would have had no chance of ever wining the war. It was a case of the North forcing Dixie’s hand. One can debate whether it was the right move or not. But one thing was clear... the CSA could not afford to just let the North station more and more troops in Dixie as that would render the attempt to resist the North moot. Consider this: if some invades your home under the pretext of “resupplying” your refrigerator and bring some friends [ who are not friendly towards you ] without your consent: you would not be in the wrong to shoot them seeing as they would be trespassing on private land.
Lincoln flat out lied to the Southern delegation in D.C. considering Fort Sumter. He manipulated the situation to start the war on purpose, willing to kill and did 600K lives to insure the Northern states dominance over the pesky South. The North could have at any time from the 1840 to the time of secession emancipated the slaves just in the same way that England did but the greed of power and political dominance by the North did not allow that option.
But there was no war at the time. The South fired the first shots.
The reason for holding on to Sumter wasn't to attack anyone or collect taxes. The reason was that so long as the US still had a foothold in the rebel territories they could claim that the union was intact. I know it may sound silly now, but it was a way the country could save face, bide time waiting for cooler heads to prevail, a way of not confronted the worst crisis and worst failure of our history head-on.
That kind of stand-off situation is something we've become very familiar with over time. It's something that a smarter, more capable Confederate government could have coped with, playing for time and jockeying for advantage as Lincoln was doing. But instead, they started the war. Don't just accept the propaganda. Consider other options that might have been available to the secessionists at the time.