I agree a lot with this article.
First, I think yes, there were far more issues than slavery. One side has tried to make the war about nothing but slavery. However, the other side has tried to dismiss this reason completely. Anyone who has read the newspapers of the time or studied the Lincoln, Douglas debates knows that slavery was an overriding factor of the time and was one of the fuses that started the whole thing. It was also a foundational piece of the economics of the South and the reason why there were trade embargoes and tariffs.
Regarding slavery, I don't believe we could have or should have done what some Libertarian's suggest and just have ‘bought’ them. That continues to justify that they were property. An individual can't be bought or sold. An individual’s greatest right is self-ownership. The government buying everyone’s freedom would have sent a message that it considered humans nothing but chattel.
Regarding how we got into the war, I believe Lincoln didn't initially see this as a legal secession but an illegal insurrection. I believe he did find justification in Article 1, Section 10 of the Constitution: “No State shall enter into any Treaty, Alliance, or Confederation...” He may have even seen this not as an initial move by the States but by certain elements within the States.
Regarding the war, things snowballed, at first it was small rebellions that built and built.. it wasn't one day everybody was happy, the next day, it was all out war.
Regarding how the war progressed and suspension of Constitutional liberty. It is hard to live in a man's shoes, but there was Constitutional authority in for many of the amendments that allowed for variance in a time of war. For example, Amendment 3 includes: “in time of peace”, Amendment 5 includes: “except in cases arising in the land or naval forces, or in the Militia, when in actual service in time of War or public danger”...
Now, as to the other Libertarian philosophical arguments, and where my Objectivist leanings differ from Libertarian thought, is that Individual Rights always trump State's rights. At that, States do not have rights, only an Individual can have a right. A State has a role, just as the federal government does. The further away from the individual, the lesser the role should be. One of the arguments for succession was the continued right of the State to subvert individual rights- the right of self-determination (ownership). There is a proper role for the Federal Government to step in IF individual rights are being subverted. States Rights(sic) are not the be-all, end-all. Individual Rights are.
Was Lincoln a tyrant? IMHO, No. He was a man caught up in extraordinary circumstances trying to make the best of the situation he was in and preserve our country.
Could he have made different decisions that would have made the war unnecessary? Possibly, but none of us (nor did Lincoln) have a magic time machine where we can jump back and forth and test different solutions. All any of us have are the choices we make with the obstacle in front of us.