Actually, the first hostile act was when Lincoln's ship, the Harriet Lane, fired upon the steamer Nashville as it was entering Charleston harbor on April 11, 1861 the day before the Sumter bombardment.
As for Virginia, the issue being discussed was the reason of its secession. I noted earlier that the fact it was being blockaded didn't exactly encourage it to stay in the union when secession came up for a vote. Another poster disputed this suggesting that Lincoln did not blockade the state until after it left, which was simply not true.
That is certainly an oversimplified version of our conversation. After the convention voted to secede militia units were mustered and federal facilities at Harper's Ferry and Norfolk seized. The rebellion had already begun in Virginia. The state government was behind it, and the referendum was only a confirmation of what had already become a fait accompli.
But to return to your original statement. Does anyone really think that if Lincoln had not extended the blockade to Virginia the referendum would have gone the other way? It's a cute debating point, but it doesn't stand up as a real hypothesis. Was secession the more justified because of the blockade? It doesn't matter so much, if the blockade was a justifiable response to the actions of the state government.
". . . an incident occurred, which I have never seen recorded, but which seems to me worthy of not. A vessel suddenly appeared through the mist from behind the Bar, a passenger steamer, which was made out to be the Nashville. She had no colors set, and as she approached the fleet she refused to show them. Captain Faunce ordered one of the guns manned, and as she came still nearer turned to the gunner. 'Stop her!' he said, and a shot went skipping across her bows. Immediately the United States ensign went to her gaff end, and she was allowed to proceed..."