My own immediate impression is of a tinfoil tablecloth stained with the juice of the grape.
Nevertheless, in between the extreme rhetoric of a bitter, disillusioned man who has also been severely disappointed in business, his POV has a certain internal coherence, and you can trace its direct descent from Jacksonian populism, and see his fury in realizing that the value system of his youth, and the public ideal that he grew up with, was being overreached by the "age of combinations" Rockefeller talked about, and the rise of the "malefactors of great wealth". This writing is shot through with pure rage. He's screwed, his countrymen are screwed, the country and its ideals are screwed, screwed, screwed, Orville Babcock is running wild, Victoria Woodhull is talking trash about Free Love, and P.T. Barnum is getting rich showing everyone the Egress. Remember, Spooner's generation grew up with the Great Revival, the beginnings of Temperance, and the abolition movement, and here the country seems to be turning into the Neo-Babylonian Empire before his eyes. I have to sympathize with him.....but still, I don't think his white heat serves him well, outside the confines of the political revival tent. Wendell Phillips, Thad Stevens, and William Lloyd Garrison all had the same problem. Stevens had to be surrounded by volunteer "bodyguards" when he spoke in the well of the House in the 1850's.
Angry flamboyancy can often leave that impression. But Spooner was constantly flamboyent and often angry, so it must not be taken as anything out of the ordinary for him. He had his own share of crackpot ideas running all around him, but in his movement he was both influential and widespread.
Now, abolitionism itself was never anywhere near the size most make it out to be and was thoroughly a fringe movement, though one that lots of people paid attention to closely.
I think the center of Spooner's complaint is with what happened to the movement's name after the war. He saw a bunch of disingenuous yankee politicians who had advocated segregation and bigotry all their lives suddenly rallying around their victory in the war and pretending themselves to be abolitionists that they were not then and never had been.
The politicians seized his movement as their own after the fact and started using it to justify their own continued political gains. Spooner being a "true believer" was naturally repulsed (as was Garrison from time to time in his dealings with Lincoln). So in flamboyant Lysander Spooner style, he lashed out with this essay.
Many of its points are little different from what southerners argued, Spooner enjoys a position that is unique to only a few - he was a northerner lashing out at the northern radical "mainstream" from a side opposite of the south yet for many of the same reasons as the south.