Here’s another take on the issue.
http://www.academia.edu/9475964/The_Myth_of_Irish_Slaves_in_the_Colonies
I disagree with the "voluntarily" part unless it was volunteer to go or get hanged for being a rebel. I can also sense the bias there. He was right about a lot of the Irish being indentured servants (which was quite bad - but wasn't always permanent and doesn't extend the punishment to the kids) with a few (not many) of them being owners.