Your question is itself unworkable for any one cause as the war it irreducably complex. Combination of causes...well, according to my own beliefs, the following roughly sums up what I think to have brought about the conflict.
1. The majority of your average confederate citizens likely took a side-with-the-homeland approach in secession and a defend-the-homeland approach in war.
2. Any persons involved in the economic activities of industrial manufacturing or agricultural production was inclined to side with one or the other for economic policy reasons. Public choice dictates that they act out of their best interests, inclining industrialists to seek protection for their industries and agriculturalists to seek free trade for their commodities. This is where the issue of the tariff and trade comes into play.
3. Persons with an economic intvestment in slaves sought the liberty to employ that investment in the territories to their benefit, whereas persons uninvested in slaves were economically motivated to oppose it due to the competition in labor slavery provided when along side free workers. Moral arguments bolstered this position, but tended to be in far smaller numbers than is often suggested.
4. An ideological battle existed on the proper role of the national government and its interaction with the states - what right did Congress have to interfere with a state's government or ensure that state's obediance to a federal policy. Constitutional arguments about the system of government and secession as a legal argument fit in here.
5. Political factions were self-interested in preserving/achieving majorities in congress for themselves. Much of the balance depended upon how many new states each region could claim as one of its own during the admittance and expansion of territories. This was a second motivation in the territorial dispute, as it could determine control of the senate.
6. Personal conflicts and emotion entered into the situation among political leaders. Persons of each side found reconciliation or compromise with the other impossible due largely to the hostility between the two, among other things. This exacerbated an already divided situation.
That's probably a fairly accurate, albeit simplified, explanation of my view of the war and its causes - at least covering the big points.
but what real and substantial improvement can you make on McPherson's short sketch?
Noting the factual error of his statements when he dismisses issues such as tariffs and economic disputes as inconsequential or non-regional.
The side with the homeland/defend the homeland approach is a given in any war, but it doesn't explain why a particular war began. Frenchmen will always side with France, Germans with Germany, but that doesn't go far in explaining the wars those countries fought. This argument, which works admirably in expaining subjective and individual factors, doesn't go far in explaining objective and collective developments. It's especially overworked when it's regarded as dangerous or damaging or divisive to seek the deeper reasons for hostilities. Politically, morally, and religiously it's a useful answer, but a historian seeking the real reasons for any war will recognize that this argument doesn't go very far or explain very much about how wars begin.
The agriculturalists of the Midwest largely backed the Union if not always the Republicans, rather than their fellow agriculturalists in the Deep South. This suggests that other factors, slavery or free soil, fear of the "slave power," ancestry and ethnicity, ideology, moral views, were stronger than any tie binding agriculturalists together against industrialists. The mass of support for the Republicans and the Union came from farmers. Moreover, powerful commercial interests had no liking for tariffs and industrial policies, either. They went with Union or Confederacy according to region.
The support for tariffs by the agricultural South under Madison and Monroe and the opposition of commercial New England to them in that period also points to the oversimplification of the argument. And agriculture vs. industry is really too simplistic to explain the kinds of alliances rural and urban people form in some conditions but not in others. Slavery looks like a strong explanation of why some groups allied and others didn't, though it's hardly the only one.
You're certainly right that those with slaves would attempt to use them to make money and those who didn't would seek to avoid competition with unfree labor. But this bolsters the argument that you claim to refute. Arguing that there's little question of morality involved says nothing about whether slavery was the key issue. Questions of blame and guilt, are not those of causation. So your point #3 backs up and agrees with McPherson's argument, though you differ on the moral context. Point #3 also goes a long way to accounting for the other points on your list.
Clearly, there's a conflict over the interpretation of the Constitution. But what fanned the conflict into war? It's possible that in time theories of constitutional interpretation could have led to another war or secession crisis. But the question is "Why this war, at this time, between these two sides?" And why did Southerners who championed American nationalism in 1812 and union in 1815 reject and try to shatter the union in 1861?
I certainly don't say that your point #4 is invalid. It helps explain why the "secession" idea ended up as a plausible option for many. And it also contributes much to explaining why the Upper South joined the rebellion (though group spirit accounts for as much, and the defense of slavery for something). But it doesn't explain why the constitutional conflict became so acute at that particular time and place. In a country with a different constitution such a conflict between free and slave areas would have taken a different shape, but it's likely that such a conflict would have occured at some point or other.
Similarly with point #5. It has some validity. But it's worth noting that the Southern states were ready to ban slavery from territories in 1787 and 1820, and this became a burning issue in the 1850s, an issue that obviously had much to do with slavery. You can argue that slavery in the territories would have been merely pro forma or de jure, but the purpose of spreading it there was to shore up the slaveholding or planter interest in the Senate. I don't think we disagree on this point. The question is the degree to which the territorial question can be divided from the question of slavery. I don't think it can.
If agriculturalism inclined one to take the side of the South on tariff and other economic questions and if this was the key issue, then there was no reason to promote the expansion of slavery into territories that would remain predominantly agricultural for generations. You can remove all moral contentious aspects from the territorial question and it still remains the question of the expansion of slavery, either on the surface (as a moral and symbolic victory or defeat for the slaveholding interest or the abolitionists) or in the depths (as deciding the real question of the fate of slavery in the nation).
With point #6 we have come full circle back to point #1. Ambitious politicians are the bane of representative government. As with siding with the homeland, political demagogues and opportunists are a constant. Why they were able to do so much damage of this particular sort at this specific time leading to this particular war is another question. Some additional factor or catalyst is necessary to join the rivalries of politicians and the conflicting interests of regions into rage and war. Point #6 accounts for the specific trend of events, but is in no way a very "deep" explanation.
Indeed, if you follow the economic analysis you do elsewhere, politicians turn out to be a minor feature. They strive to succeed by appealing to the interests and passions of others. They may heat up existing passions. They may benefit existing interests and hurt others. But they are working with forces and interests that are already present when they enter the scene. Though politicians can do great harm, they aren't part of a "deep explanation," but of more superficial and adventitious causation. They do matter, and a bad law can do untold harm, but if you're looking for a "deep explanation" you won't stop at the level of floor fights and committee meetings.
The question of whether any political compromise could have prevented the war is an important one, but the true source of the conflict was elsewhere. One could give some credence to your view depending on how one defines "cause" -- that's not relativism, either, but an important question of methodology that gets left out of debates like these -- but it's clear that if one uses cause as McPherson does, point #6 isn't much of an argument.
DiLorenzo has characterized his view as a "public choice" analysis, but it really doesn't look like much of an improvement over Charles Beard's economic interpretation of history. We all know that people tend to act in their own best interest economically. That's the beginning of analysis. The end product has to be more subtle than that. Moreover, such an analysis is only a tool, not a hard and fast method that provides one unique answer for every specific problem.
DiLorenzo's view is a very partisan and partial analysis of the economic phenomena leading up to the war. And DiLorenzo's analyis doesn't avoid the kind of moral outrage that he criticizes in Unionists. It simply transfers the object of hostility from slavery to tariffs. DiLorenzo throws out one set of moral arguments as red herrings or distractions or cover for economic interests, but he doesn't perform the same operation on other moral arguments. This is a result of the libertarian "metaphysics" which discounts non-libertarian arguments. Unfortunately it's also a skewed perversion of libertarian philosophy, which downplays some eminently libertarian principles.
Finally, I probably erred in characterizing the view in McPherson's article as a "single cause" theory. "Root cause" would be a more accurate formulation: slavery as the taproot of the conflict, with other roots feeding into it to produce the war. "Single cause" -- or even "root cause" theories turn many people off, because they look simplistic, and also because they can be used to put all the blame or guilt or responsibility on one side. There is a rawness or barbarism about such interpretations that demands qualification and refinement, but they can contain much truth and explanatory force.
I suppose McPherson's article fails as sophisticated history and nuanced history, but it's not meant to be that. As a sketch arguing a thesis with much truth in it, it's hard to refute. You can build on it, polish it and fill it out, reject some parts and bring in other factors, but it's worth reading and thinking about for it does capture an essential truth about the war's origins. Not the essential truth, though. But no historian can do that or would claim to.
You have mentioned factual errors in it. Have you found any?