Because, as has been shown in the debate on this thread, that is not true (i.e. "a lie").
Something i've learned in life, is that when people are lying and covering things up, they aren't the good guys.
When you find both sides are lying and covering up, you learn there are no "good guys".
"Winners write the history books" is a truism.
The idea one side is all good, and the other side is all bad, is a ridiculous simplification.
Except that it was true and the denial of it is the lie
South Carolina Congressman Robert Barnwell Rhett had estimated that of the $927,000,000 collected in duties between 1791 and 1845, the South had paid $711,200,000, and the North $216,000,000. South Carolina Senator James Hammond had declared that the South paid about $50,000,000 and the North perhaps $20,000,000 of the $70,000,000 raised annually by duties. In expenditure of the national revenues, Hammond thought the North got about $50,000,000 a year, and the South only $20,000,000. When in the Course of Human Events: Charles Adams
As Adams notes, the South paid an undue proportion of federal revenues derived from tariffs, and these were expended by the federal government more in the North than the South: in 1840, the South paid 84% of the tariffs, rising to 87% in 1860. They paid 83% of the $13 million federal fishing bounties paid to New England fishermen, and also paid $35 million to Northern shipping interests which had a monopoly on shipping from Southern ports. The South, in effect, was paying tribute to the North.
"Before... the revolution [the South] was the seat of wealth, as well as hospitality....Wealth has fled from the South, and settled in regions north of the Potomac: and this in the face of the fact, that the South, in four staples alone, has exported produce, since the Revolution, to the value of eight hundred millions of dollars; and the North has exported comparatively nothing. Such an export would indicate unparalleled wealth, but what is the fact? ... Under Federal legislation, the exports of the South have been the basis of the Federal revenue.....Virginia, the two Carolinas, and Georgia, may be said to defray three-fourths of the annual expense of supporting the Federal Government; and of this great sum, annually furnished by them, nothing or next to nothing is returned to them, in the shape of Government expenditures. That expenditure flows in an opposite direction - it flows northwardly, in one uniform, uninterrupted, and perennial stream. This is the reason why wealth disappears from the South and rises up in the North. Federal legislation does all this." ----Missouri Senator Thomas Hart Benton, cited at page 49 of The South Was Right!, by James Ronald Kennedy & Walter Donald Kennedy
It has not been "shown." It has been alleged. The evidence contradicts that. I have real number evidence to prove the point. The other side has obfuscation.
The 72% of the total revenue for the government came from the South. Now you can jump through hoops pretending the North paid some of that, but the reality is that that money came out of the South's pocket, not the North's.
The idea one side is all good, and the other side is all bad, is a ridiculous simplification.
Yes, i'm sure the Nazis had some redeeming characteristics, though I could not put my finger on what they were. I suppose them killing a lot of Communists could be seen as a good thing, but they weren't really doing it for a good reason. In that regard they are kind of like Lincoln invading the South. It may have had some good results, but it wasn't the reason why he was doing it.