As bad they claim they had it in those days, it was not remotely comparable to living in slavery.
Consider this. Look at how many of those immigrants came to the US, got a job in a mill or mine, saved some money, and then sent back to the old country bringing friends, family, in some cases nearly entire villages over to join them.
If conditions were that bad, would they have done that? I don't think so.
Do you remember the famous "rumble in the jungle" and what Muhammad Ali said when he got home and they asked him what he thought of Africa?
I don't remember the whole quote but the gist was that he expressed gratitude that his ancestors got on a slave ship bound for America.