Not entirely. The additional contents of that "at worst" scenario was a horrific cost in human lives (some 600,000 total), the physical economic destruction of a country by a bitter war, and the increasing centralization of power in Washington and away from the state and local levels.
And still an absolute good came out of it.
That single absolute good was among many unnecessarily pursued absolute horrors.
This Spooner almost seems like he wants the South to be congratulated for at least being honest scumbags.
His statements toward the south reflect their consistency and their attempts, at least in idea, to adhere to their claimed root principle - the idea of self government. Spooner detested slavery and fought for its abolition all of his life. But he also recognized that achievement of that abolition on fraudulent pretenses and at a horrific cost with equally appalling yet wholly unnecessary evils accompanying it was itself a moral wrong. According to the logic of ethical conduct, moral ends are spoiled when they are achieved by immoral means. Spooner, a man whose devotion to the abolition of slavery was without question, recognized that and called Mr. Lincoln's war what it was - an unnecessary and brutal sham.