Indeed, to look at 19th Century American through the eyes of the secessionist fire eaters gives the opposite conclusion to that which 21st century observers reach. To the militant secessionists, the United States were headed rapidly towards racial equality and "amalgamation." They condemned the union for that reason. Though one can and should reject their value judgement, their assessment of what Republican victory meant ought not to be forgotten. It makes 19th century America look far better in terms of 21st century ideas than many people today would give it credit for.
In other words, the Confederate judgement of how bad the Union and the Republicans were would be taken as a very positive assessement by current egalitarian standards. The present day assessment of how bad North and South both were in terms of race doesn't account for the passionate fear and loathing for the Union, the abolitionists, and the "Black Republicans" on the part of many who supported the Confederacy and the Democrats, largely on racial grounds.
Also, if we want to understand the questions at issue in the 1850s and 1860s, racial equality has to be pretty far down the list compared to slavery and its expansion. That era was talking primarily about slavery. Recasting the debate in terms of racial equality and giving both sides a failing grade is a pretty late 20th century view in itself.
I think we can respect military skill and courage even if exercised in behalf of a cause we reject. One sidebar: Stonewall had a lot of the traits that are condemned in Grant and Sherman. Arguably, he was less of a cavalier than any major commander on either side. His puritanism gives him a lot of the traits in Yankee character that neo-confederates attack. Indeed, contrary to the caricature of noble Southerners and brutish Northerners, successful and distinctive commanders on both sides had much in common. Why should they not, as they came out of the same culture? Discuss.
First, I don't think I've ever seen Stephens classified as a "fire-eater" until now. Your attribution of beliefs to the "fire-eaters" is also inconsistent with a good ammount of their literature and commentary. Consider the following from perhaps the greatest of the "fire-eaters" and indisputably their leader in congress. He said it was economics that led him to conclude secession's inevitability, not some concept of racial equality allegedly promoted by Lincoln.
"You suppose that numbers constitute the strength of government in this day. I tell you that it is not blood; it is the military chest; it is the almighty dollar. When you have lost your market; when your operatives are turned out; when your capitalists are broken, will you go to direct taxation? Burn down a factory that yields ten, fifteen, twenty, twenty-five thousand dollars a year to its owner and he goes to the wall. Dismiss the operatives, stop the motion of his machinery, and he is as thoroughly broken as if his factory were burnt; for the time he is bankrupt. These are matters for your consideration. I know that you do not regard us as in earnest. I would save this Union if I could; but it is my deliberate impression that it cannot now be done....
Your irrepressible conflict is predicated upon the supposition that this is a consolidated Government; that there are no States; that there is a national Government, as they call it; that the people who live between the two oceans and between the Gulf and the lakes are one people; that the boundaries of Massachusetts have, by some hocus pocus, been extending themselves until they embrace all the remainder of the Union; and that we are one people, have a national Government, and are under the control of "the Massachusetts school of politics," as the Senator from New York said he was. This is the fatal error." - Sen. Louis T. Wigfall, December 1860