Since when does the Supreme Court have to "okay" every action of another branch of government?
The Supreme Court is not called upon to "okay" every action of another branch of government.
However, in the case of Merryman, by properly brought suit, the decision of the court was rendered upon the UNCONSTITUTIONAL actions of the Constitutional rapist known as the Great Usurper, Abraham Lincoln.
In cr #1685 you said, "No Supreme Court ever directly ruled on the constitutionality of Lincoln's action with regard to the suspension (of the privilege of) the writ of habeas corpus."
To the contrary, by an In-Chambers Opinion of the Chief Justice of the Supreme Court, the Constitutional rapist known as the Great Usurper Abraham Lincoln was speicifcally given chapter and verse of the history of the law and informed precisely and specifically how and why he was in violation of the Constitution.
As Chief Justice Rehnquist observed on page 44 of All the Laws But One,
Following Lincoln's justification, in his July 4 speech to Congress, for disregarding Taney's Merryman decision, [Attorney General] Bates issued an opinion justifying the President's action. It was not a very good opinion. It essentially argued thateach of the three branches of the federal government established by the Constitution was coequal with and independent of the other two. The President was thus not subordinate to the judicial branch, and so the latter could not order him, or his subordinates, to free Merryman. This proposition had been refuted by Chief Justice Marshall's opinion in Marbury v. Madison more than half a century earlier.
The Constitutional rapist known as the Great Usurper Abraham Lincoln was well aware that his actions were UNCONSTITUTIONAL, but his lust for power was such that he did not care and he proceeded to rape the Constitution he had sworn to uphold.