And one can easily overestimate how horrendous conditions were for 19th century free laborers - yes, they sucked, but they had options and mobility and that - even before strikes and unions started serious improvements - made being free preferable. I'm a firey Socialist, but comparing free labor to slavery is consistently in the former's favor in all but the most ideal conditions for the slave or the nastiest for the free.
Yeah, good point there, IMHO.
Plus, slavery wasn't all about economics. There's also the social factor - both the prestige of being a slave owner, the convenient means of control of part of the population,
Very true, as I think that might be one of the reasons that slavery could struggle on well into the 20th Century in the Confederacy, even if it no longer thrives.
and then there's the poor whites.
....and here's one of potential ingredients for it's ultimate downfall;
As I've mentioned earlier, even though most non-wealthy whites didn't exactly
like the blacks, slave or free, many of them would still keep their best interests in mind, including those of their finances:
In OTL's antebellum South, there was very, very little in the way of a middle class outside of perhaps a few of the more notable cities(Richmond, Charleston, New Orleans, and maybe Memphis and Birmingham later on); poverty was endemic in many areas, and in fact, it was so bad in parts that it was a primary reason for emigration fin the 19th Century, and primarily north and westward(I have a fair number of Southern ancestors who did just that, btw; many of them ended up in Kentucky, Indiana, and Illinois in particular).