It certainly was to Lincoln; he brought it up himself in conversation. And it certainly was to people in New York City, whose newspapers' editorials record the collective gasp of realization that went up as the Southern States began to leave the Union.
These arguments evolve amongst those that look to either blame or absolve the North or South.
Well, the principal dialogue is between the incriminators, like McPherson, who have a further political agenda (they would call it "applying lessons learned" or something like that), and the traditionalists who are arguing back against the Marxists' revisionism and their sometimes implicit, sometimes explicit moral accusations against the South, Southern leaders, or more to the point, modern white Southerners.
McPherson and his fellows are engaged in attempting to fix a scarlet letter of their own devising on Southerners, for their own purposes. Naturally, some of the Southerners are resisting indignantly.
Lincoln did not declare war on the South. The South declared war on the North and did so via arms without a chance at negotiations. The South did not reject the North over tariffs and Lincoln did not fight the war over that issue either.
That Lincoln may have mentioned it in passing is noted. I am also sure Lincoln mentioned the price of cotton in London markets on occasion but that is not why the war was fought for either.