That is definately one thing that I have to agree with. He didn’t realize taht while slaves were good, there were also the bad types that were also freed. If Lincoln had seen the reality of the system, then I am sure that he would have understood a lot more than he did when he started that war.
OTOH, the new european immigrants would work cheap, do dangerous jobs, and if they got killed, just hire another. Sure, you paid them, but you either got that back through the company store, housing, etc., or they had to fend for their own sustenance using those wages.
The harsh reality was that the cheap immigrant labor was cheaper in the long run, especially when the downside of incorrigible slaves was factored in.
I think slavery would have died a natural death ere long, even without the war.