[DiogenesLamp]

If you read further, he answers that question. His answer is pretty much what I've been saying.

Slavery was just an excuse, and it was really about political, and consequentially economic power.

Also there were only four states (out of 11) that cited slavery as a reason for leaving, and in some of those, it wasn't even the most important reason for doing so.

[SoCal Pubbie]

I did read further. Those excuses were the words of Robert Toombs, not the author, whoever that is.

[BroJoeK]

DiogenesLamp: "Also there were only four states (out of 11) that cited slavery as a reason for leaving, and in some of those, it wasn't even the most important reason for doing so."

Of the first seven seceding states, four issued "Reasons for secession" documents.

1. 1st out, South Carolina (12/20/1860): mentioned no reasons other than slavery.
   "On the 4th day of March next, this party will take possession of the Government.
   It has announced that the South shall be excluded from the common territory, that the judicial tribunals shall be made sectional, and that a war must be waged against slavery until it shall cease throughout the United States."

2. 2nd Mississippi (1/9/1981) mentioned no reasons other than slavery.
   "Our position is thoroughly identified with the institution of slavery-- the greatest material interest of the world."

3. Florida (1/10/1861) listed no reasons period.
4. Alabama (1/11/1861) Ordnance of Secession mentions only slavery.
   "Whereas, the election of Abraham Lincoln and Hannibal Hamlin to the offices of president and vice-president of the United States of America, by a sectional party, avowedly hostile to the domestic institutions..."

5. Georgia (1/19/1861) Reasons for Secession focuses primarily on slavery and does not mention either tariffs or taxes, but does complain about bounties for fishing smacks and other such Northern "aggrandizements".
   "A brief history of the rise, progress, and policy of anti-slavery and the political organization into whose hands the administration of the Federal Government has been committed will fully justify the pronounced verdict of the people of Georgia.
   The party of Lincoln, called the Republican party, under its present name and organization, is of recent origin.
   It is admitted to be an anti-slavery party."

6. Louisiana (1/26/1861) listed no reasons period.
7. Texas (2/18/1861) focused primarily on slavery but does also complain, saying Secretary of war Jefferson Davis' new army brigades (1856 -- R.E. Lee 2nd in command) sent to protect Texans against "Indian savages" and Mexican "banditti" did a lousy job of it.
   Texans said nothing about taxes, tariffs or bounties to northern industries.
   "In all the non-slave-holding States, in violation of that good faith and comity which should exist between entirely distinct nations, the people have formed themselves into a great sectional party, now strong enough in numbers to control the affairs of each of those States, based upon an unnatural feeling of hostility to these Southern States and their beneficent and patriarchal system of African slavery, proclaiming the debasing doctrine of equality of all men, irrespective of race or color -- a doctrine at war with nature, in opposition to the experience of mankind, and in violation of the plainest revelations of Divine Law.
   They demand the abolition of negro slavery throughout the confederacy, the recognition of political equality between the white and negro races, and avow their determination to press on their crusade against us, so long as a negro slave remains in these States. "

Two other "reasons for secession" documents are worth mention:

• South Carolina -- Fire Eater Robert Rhett's December 1861 address says more about slavery than any other reason, but does go on about Britain's 1776 taxes, comparing them to 1861 US taxes.
  Rhett says nothing specific about tariffs or "bounties".
  "The people of the South have been taxed by duties on imports not for revenue, but for an object inconsistent with revenue -- to promote, by prohibitions, Northern interests in the productions of their mines and manufactures."

  Of course, those duties would also promote "mines and manufactures" in the South, had Southerners been interested.

• Georgia, CSA VP Alexander Stephen's "Cornerstone Speech" March 21, 1861 puts the case as clear & simple as can be imagained:

  "Our new government is founded upon exactly [this] idea; its foundations are laid, its cornerstone rests upon the great truth, that the negro is not equal to the white man; that slavery -- subordination to the superior race -- is his natural and normal condition.
  This, our new government, is the first, in the history of the world, based upon this great physical, philosophical, and moral truth.[1]"

So yes, it was all about "slavery, slavery, slavery" with some other miscellaneous complaints mixed in, more or less as seasoning.