Also, wouldn't ending slavery mean the South gets more representation? They'd get to count the other 2/5 of the population. (Some of the freedmen might go north, but still).
3/5 Compromise dictated the number of allotted Representatives that slave-owning States would get, because House Delegates and Electoral College count were a function of population. Your comment here is rather tone-deaf and I don't think you thought it through completely.
Slaves could not vote in the South, so the representational "weight" of the slaves was a State-level communal asset enjoyed by the voting populace as a function of having more votes in the House of Representatives and Electoral College.
Once slaves were freed and able to vote, the representational weight of the Southern States as a function of House Delegates and Electoral College count did indeed increase... but the votes of the land-owners and former slave-owners were cancelled out by the enormous increase in former slaves that could now vote and may not vote in the same manner as the former slave-owner. Which was the whole reason for the Jim Crow laws and voter intimidation/suppression actions of certain groups.
I think you might want to check your sources on this post. Off-shoring the freedmen was certainly on the table in those days, but was it really the favored solution of "most" abolitionists?
I'm content to be challenged on that; it's been awhile since I've read anything about the Civil War and Abolitionist movement. My stance is based on content I encountered and could be weighted by anecdotal experience rather than comprehensive analysis. Then again, the same could be same for your rebuttal.
Finally, was slave labor really a threat to Northern manufacturing? The North seems to have been doing just fine on that score. Or do you refer to mechanized farm implements? I thought that was largely a post-war development. Tractors came along decades later, right?
The first "combine" was the McCormick Reaper, invented in the 1830's.
https://www.britannica.com/video/226769/why-was-the-McCormick-Reaper-so-importantWhen grain was harvested by hand, a huge number of laborers were required. A farmer who didn’t have enough people to complete the harvest had to either accept crop loss or pay exorbitant wages to hire peak-season workers. The McCormick reaper offered hope to farmers that the yield of their fields might no longer be limited by the number of available farmhands. Over the next few decades, news of the invention spread to every part of the United States—and even across the pond to England and France. By 1856 McCormick was selling more than 4,000 mechanical reapers to farmers each year.
1849 saw the introduction of the first commercial chemical fertilizers. John Deere and others started offering interchangeable blade plows around this time, and the 1860's saw the introduction of gang plows with multiple bits able to produce multiple furrows.
Lots of this tech depended upon animals to make use of, but they were absolutely labor savers and cut dependence on either hired hands or slaves. And predominantly manufactured and sold by Northern industrial centers.