Maybe you never read about the thousands of Irish who died building just the Erie Canal. Now multiple by the thousands of canal projects going on in America pre-Civil War.
Slaves were property and were valuable asset to a slave owner. The owners took decent care of slaves as a dead slave was worth nothing and too many dead slaves would lead to bankruptcy.
The Irish? Let them die. There are thousands of more desperate for a job. The canal owners could care less if they died by the thousands - which they did - over and over.
And then the Irish (unlike slaves) were then drafted and died by the thousands in the Civil War.
All in all - who had it better????
all in all, both situations sucked... who had it better? the one who had freedom had it better, yes? recall these words, "give me liberty or give me death?" (Patrick Henry)