That's an interesting assertion, but also one that is unfortunately for you contradicted by the historical record. Look at his private letters if you doubt me. Practically every one of them on Sumter was stamped and sealed with confidentiality as part of his carefully controlled correspondence between a select group of allies who were doing his bidding at the time in Washington.
Check the letters circulated during late December and early January among Lincoln's circle of allies - William Seward, Lyman Trumbull, Hannibal Hamlin, Winfield Scott, Thurlow Weed and a few others. They are consistently sealed in strict confidentiality including many with enjoinders that Lincoln's name be kept out of the dealings of his bidders even though they were acting on his behalf.
Confidentiality was an overriding concern throughout the correspondences. That seems to be an unusual concern for somebody you allege was willing to say it all out in the open, does it not?
Publicly Lincoln did begin to make the case that the forts were his, often sugar coating it as a political argument under the guise of "preserving the union." In some cases when he had a friendly audience, he was more open about his reasons - pledging revenue collection. But his public speeches simply do not compare to the military planning he was engaged in behind the scenes.