As secession isn't specificly mentioned in constitution it would then fall under 10th amendment.
Shakes head sadly....
As has been stated over and over, I know this is what you "feel", but you are wrong. And that is not my opinion. Its the opinion of the Supreme Court, which is the definitive source for what the Constitution says. So its irrelevant what you "feel". You can say this over and over til your face is blue (and I am sure you will), but it still will not change reality.
Now, if you want to argue that folks didnt know that before secession, you would have a valid argument. All the more reason why I keep saying if South Carolina felt they had a right to secede, then they should have filed suit instead of opening fire and trying to kill people. Maybe they would have gotten a different result, but probably not. We know Taney, who was very pro-southern and pro-slavery, thought it was illegal. If you don't have Taney, then its hard to imagine how you get a majority.
And I suspect South Carolina knew their argument was weak and that is why they avoided going to Court.
And as for the "legal scholars" who claim it was incumbent for the US to go to Court to say the right did not exist, that is simply not true and not how the Courts work. In areas where this is room for interpretation the President also has the obligation to interpret the Constitution as he sees fit (always subject to being overruled by the Courts), and act accordingly. This happens all the time when you dont have cases on point. And if you think they government is wrong, then you go to Court to get an injunction against it. This is how it has always worked, even up to today. So if Lincoln, as President, thought secession was illegal, he could act on that interpretation until the Courts told him otherwise.
Not to mention, its laughable to think of the US getting an injunction against South Carolina, and then delivering the injunction to the Governor, and the Governor saying "Oops, my bad. Guess we were wrong. Nevermind." Does anyone really think South Carolina would have cared what the Supreme Court said?
Conversely, a statement that Secession was legal would have had significant impacts against Lincoln's ability to carry on the war. Its hard to imagine Lincoln being able to prosecute a war that the Supreme Court has ruled was illegal. It would affect northern support for the war, subject draft boards to injunctions to stop the draft, and it likely would have given foreign powers a stronger basis on which to intervene. Is it possible Lincoln goes ahead anyway? He might try, but he would have been severely hampered and I think we would view him and the war much differently than we do today.