"I’d rather be a rebel than a slave." —Emmeline PankhurstThe warriors claim this is racist, that "slave" is code for "black."
Short reply: tell it to Spartacus.
Or to the Slavs whose enslavement lies at the root of "slave".
Many people who have not studied history think the "one drop" rule was always the distinction between who was white and who was black, but it was a creation of Jim Crow. During the era of legal slavery, whiteness varied from state to state: in most, if you were 3/4 white, you were white. But to be a slave, the only requirement was that your mother was a slave, so there were slaves in the Old South who were legally white, and it's likely some of their owners were legally black.
As for the ongoing argument over whether the Irish were slaves, if you're not free, you're a slave. Indentured servants and prisoners of war who were forced to work were slaves, and if they died before they were free, they died as slaves. Being indentured was not necessarily better than being a slave; as noted at Were the Irish Slaves? | HistoryNet: "In practice, the masters sometimes extended the time of indenture; others, for whom the indentured servant was not the lifelong investment that a black or native American slave was, had no compunction about working the indentured servant to death in his last year."
White Slaves – The Multiracial Activist
The 'white' slave children of New Orleans: Images of pale mixed race slaves used to drum up sympathy and funds from wealthy donors in 1860s | Daily Mail Online
Appropriation alert: no one owns the metaphor of slavery
Poor whites in the USA