Because this is where people's logic falters. If the Southern States didn't have the right, nobody has the right. Never again will anyone ever have the right.
The Philosophical foundation must go through that nexus of history, because there is no way to avoid it. If such a right exists, by every reasonable criteria they met it.
Therefore, you either have to demonstrate how their right to leave is substantially different from the Founders right to leave, or conclude that they were denied their right to leave.
any number of your friends have a "right" to declare independence
And here, once again, is the deliberate derogatory comparison of Nine Million people to "any number of friends".
Lincoln doesn't need me to defend him. He remains very popular.
Because he has had all the people he's ordered about (and their descendants) defending him ever since he ordered them about.
This is not complicated. Once he got into power, he had the authority to order one group of people to hate another, and if they didn't obey that order, they were cashiered or worse.
People say our military will not harm us. They say it is filled with good and decent people who will not obey orders to do something evil and wrong, yet we see Officer after Officer rolling over regarding matters of the most significant interest to the United States, and meekly obeying the most rank idiocy dictated by that current fool in the White House.
They will implement "Gay appreciation month" and say "Yes Sir! May I have more Sir?!" They will attack Chaplains in the Army for doing their Job. They will war-game "Tea Party" Americans as enemies and produce plans to attack and destroy them. Nuclear Iran? "Yes Sir!!!" May we give them our bombs Sir!?"
The same social dynamic worked during Lincoln's reign too. A Liberal President splits the nation, and then uses the forces of the Several states to smash any effort to leave his control, and at horrible costs to the nation.
He's just had very good propaganda ever since. He's also left people needing to justify their own actions, because he forced them to do his bidding. They cannot stomach the thought that they have done something wrong, even when they did. They would rather believe that what they did was right, because they are not "bad" people, and so this is what they believe. Nobody wants to believe they were led by a dictator. Ask the Germans how they feel. Had they won, Hitler would be just as popular as ole Abe Lincoln.
There is a sort of Psychological denial going on, and it has been inherited by a large number of people, and for the same reasons as it worked on their ancestors.
I suspect you're right about that, but I really don't know.
What I can say is that none of the twenty-first century issues that you're complaining about in that post are the fault of Lincoln (who died 150 years ago) and none of those issues should preclude you from living a happy, successful life here in the United States.
Life can be good. ;-)