Hogan did a Q&A on Medium that might be worth checking out where he goes into more detail on the claims made in White Cargo specifically. A lot of the "white slavery" thing seems to go hand in hand with Holocaust denial as a big white supremacist thing; I'm not accusing you of that, though. I suspect the narrative is comforting but it also plays into the idea that chattel slavery wasn't uniquely horrifying.
I'll willingly concede that chattel slavery and indenture weren't all that different up until the late 17th century, by the way, mainly because no one really lived long enough for it to matter. But once the surplus population of England was needed for industry so there wasn't enough labor to meet the growing demand for tobacco, and people in the colonies were living longer so servants were reaching the end of indenture, it took on a qualitatively different character (particularly in law). Black slavery became the only means to provide that labor so a trickle of blacks slaves turned into a waterfall, and racism became an ideological means by which a group of people could be cut off from Lockean conceptions of freedom or liberty.
A good book (rather two books) on this is Ted Allen's Invention of the White Race, though there's a shorter "summary of the arguments" available online (Google summary of the arguments of invention of the white race). Allen did extensive primary source research on Virginia and Ireland. His primary rhetorical flourish is to show that the racial power structures used under the Protestant Ascendancy in Ireland are the same as in Virginia, with Protestants and Catholics taking the place of white and blacks. In other words, there's no biological "races," they're invented for political purposes. In the US the marker was skin color and in Ireland religion, but other countries in the Americas had a very different racial power structure despite a history of chattel slavery (in Jamaica, for instance, there's a difference between black and "colored" that doesn't exist in the US).