If you are citing the Washington Post, you have already lost the argument.
Just for kicks, I looked at the arguments of the Vermont Liberal Sociology (not History) Professor. He gets a few things right, but some of the essentials he gets absolutely wrong.
The "Tariff" is a misrepresentation of the real issue. Yes, the South was paying 3/4ths of the Tariff revenue, but that is not the larger aspect of the economics involved.
The larger economic issue was the 40% of all value which New York was siphoning off from Southern exports through their Shipping, Banking, Warehousing and Insurance monopolies. The manner in which New York had focused nearly all European trade to flow through their City is clearly Illustrated by this map.
The fact that 3/4ths of that money represented by those Coins over New York was created in the South, was not lost on the Southern businesses that created that wealth. (Yes, through slavery.) Independence would let the South gain 3/4ths of that trade money represented by those tariff collections, and it would also mean that the Wealthy and Powerful Robber Barons who backed Lincoln for the Presidency would not only *LOSE* that money, but would also face newly capitalized Southern Competition for their own existing Industries.
The Fact is, Southern Independence would have been economically ruinous to the Wealthy Northern Interests as well as directly ruinous to the Union Federal government revenues.
The money involved, representing a large chunk of the total economic activity of the North Eastern States, was easily enough of a reason to launch a war to Stop this threat to their interests by stopping the Independence that was causing it.
As Anti-Slavery Author Charles Dickens noted at the time:
…the Northern onslaught upon slavery is no more than a piece of specious humbug disguised to conceal its desire for economic control of the United States.…Union means so many millions a year lost to the South; secession means loss of the same millions to the North. The love of money is the root of this as many, many other evils. The quarrel between the North and South is, as it stands, solely a fiscal quarrel.
Southern Independence was a Deadly financial threat to the power blocs of New York/New England, and *THAT* is why there was a war.