It was an unreasonable of Lincoln to expect that a fleet of warships from a hostile power would be permitted entry into Charleston harbor. Their mission, which included orders to fight their way in when they were inevitably refused entrance, was one of inherent hostility. The simple fact is that without Lincoln's fleet there would have been no bombardment. It was the direct and causal instigating event.
Why not since he gave clear explanation for the purpose of the trip? He didn't sugar coat anything. He made it clear that they were there to land food only. To maintain the status-quo. Not to force anything. They were not out to invade Charleston or take any hostile actions, unless hostile actions were taken by the south first. That was made perfectly clear in the letter to Governor Pickens. But the status-quo was not in the Davis regime's interest. And the only inherent hostility was on the part of the southern forces, who shot at anything flying the Stars and Stripes.
Apparently the constitutional election of a Republican as President of the United States was a direct and instigating event to southern Democrats like Governor Pickens. His inaugural address in Dec 1860 makes that clear enough.
Who fired the first shot?
President Lincoln maneuvered the rebels into opening hostilities. But he didn't shy away from a confrontation. He sincerely thought the rebellion would collapse if firmly opposed.
One point that ought to come out is that opposition to secession in the north was not well focused in early April. Life went on in the north; who cared much what the south did? As is often mentioned, New York City seemed to support secession.
But once the rebels fired on Old Glory, it galvanized the nation, one author has suggested, much in the same way that the attack on Pearl Harbor did.
There was a large and active anti-war movement in the U.S. prior to 12/7/41. The next day, it was gone.
So President Lincoln's actions got him what he wanted -- he thought.
Walt