Those were not the last orders Anderson received. The ones you cited were the ones Buchanan objected to. From Buell's orders you quote [my red bold underline below]:
... an attack on or attempt to take possession of either one of them will be regarded as an act of hostility, and you may then put your command into either of them which you may deem most proper to increase its power of resistance. You are also authorized to take similar defensive steps whenever you have tangible evidence of a design to proceed to a hostile act.
You and I had a discussion of this when you were posting under your previous handle. I kept asking you where the mob was or the attempt to take possession of Moultrie that might justify Anderson's move if he went by Buell's orders. You never could provide evidence of one.
Charleston officials had promised to stop any mob attacking Fort Moulrie, and they had boats patrolling in the harbor off Fort Moultrie to prevent an approach from the water. Anderson's own officers said that the modifications they had made to Moultrie were sufficient to protect them from a mob, but not an organized army. What soldiers attacked Moultrie?
Here is an excerpt from Buchanan's December 21 revised order to Anderson sent by Floyd:
It is neither expected nor desired that you should expose your own life or that of your men in a hopeless conflict in defense of these forts. If they are invested or attacked by a force so superior that resistance would, in your judgment be a useless waste of life, it will be your duty to yield to necessity and make the best terms in your power.
Anderson was certainly invested, i.e., enclosed or surrounded, by superior forces, although they had not moved against him.
Anderson's move to Sumter also violated another of the tenants of Buell's instructions, to wit:
You are carefully to avoid every act which would needlessly tend to provoke aggression; and for that treason you are not, without evident and imminent necessity, to take up any position which could be construed into the assumption of a hostile attitude.
Anderson's move was certainly construed as hostile, as the report from the Charleston Courier I provided above indicates. His move stopped negotiations between the South Carolinians and Buchanan and led eventually to open conflict.
tenants = tenets
You might have added that Lincoln was kibitzing and nibitzing from the sidelines betimes. From his election forward, he was communicating directly with Gen. Winfield Scott and members of the Northern "war faction" (I would call them) of Buchanan's cabinet, which you'll recall already included the notorious South-hater Edwin Stanton. Stanton became Attorney General (having had another cabinet post up to that time) just days before public accusations of improper handling of government bonds were brought against two Southern members of the Buchanan cabinet (they were pushed out in disgrace -- just like Obama today does with heterosexual Army generals). They left just before the end of December, 1860.
Former Michigan senator Lewis Cass, a "peace Democrat" and sometime co-sponsor with Stephen A. Douglas of the "popular sovereignty" doctrine, resigned his cabinet post at the same time and retired from public life.
You people do love confusing me with other posters.
Those were not the last orders Anderson received.
Yes, let's look at those. The part you seem to focus on is where Floyd said, "It is neither expected nor desired that you should expose your own life or that of your men in a hopeless conflict in defense of these forts. If they are invested or attacked by a force so superior that resistance would, in your judgment be a useless waste of life, it will be your duty to yield to necessity and make the best terms in your power." You seem to read that as meaning Anderson should take no steps at all other than stay where he is and await attack. But in those same instructions Floyd also said, "You are to exercise a sound military discretion on this subject." I would take that to mean that Anderson should take the steps necessary to safeguard his command. It's pretty apparent that Anderson took them to mean the same thing.
You say there was nothing to justify Anderson's move. That is incorrect. Accounts I've read detailed that people like James Petigru warned Anderson that the militia was gathering and that the forts would be taken by force if necessary. In his letters of December 22nd Anderson talks about reports of a steamer stationed between Moultrie and Sumter and his belief that the ship was meant to prevent him from moving there. In his letter to his superior on the same date, Captain Foster was even more specific identifying the number of steamers and the veiled threat offered by the men on one of them in respose to a challenge. Five days later, Captain Foster said he saw evidence that an attack was imminent somewhere and was told it wasn't safe to remain in Charleston.
You may not feel that this was sufficient reason for Anderson to make the move to Sumter. But it's always easy to armchair quarterback, and rather than second guess the main on the scene I feel it's more prudent to trust that Anderson did believe his command was in danger of attack and that the move to Sumter was the only logical move to prevent his men from being killed or captured.