I would think it is a fundamental philosophical thing, Lincoln exacted that in one nation there will be one law and folks will enjoy equal protection under that one law.
Sure, states could still dabble in the small stuff, but in a broad sense, Lincoln precipitated one nation, one law.
Lincoln haters(or those rating lincoln low) prefer (it seems) that fiefdoms can benefit from a nation state for purposes of international conflict, but not oblige towards any sort of commitment of morality and law.
It is a sensible notion at first, but in the absence of even one well-maintained state to achieve this, I am thinking it is more a consequence of fantasy than reality.
I am unaware of a cohesive nation that at once defends national boundaries but varies so widely on its interpretation of rape, torture, murder and so on.
In the absence of a commonly held morality, enforced by common law, it seems such states are absent from the historical record, and are likely the product only of over-active imaginations ... am I to really fight and die so that people are afforded the right to rape and kill in my union ... or do I require a code of conduct for membership, and entirely withhold support in the absence of that? Lincoln required a uniform code of conduct. The consequence was the erosion of states rights. Some lament that. Others prefer, at least at the fundamental level, a uniform code on fundamental moral and legal questions as a component of membership. A good argument can bee made for having "let them go" or, indeed, kicking them out now. But that would remove this discussion from the context of a national president.
History is full of the balkanization examples, I am not sure if it is full of successful examples of nations without something resembling a common moral compass described by and enforced by law. The notion that some member states prohibit rape, torture and murder and that others condone it seems to me to spell only doom in term of the maintenance of a successful nation.
We have to be able to agree on when it is or is not ok to rape and murder people, it is a necessary prerequisite to establishing or maintaining a nation state. A number of states felt rape and murder was a local matter, to be determined by skin color, other state required a consensus on this for membership.
That they required membership at all falls outside the measure of presidential ranking to me, it is as if we had to include King George in our measure of presidents.