As the article states. Slavery is an aspect of Roman society that is so often hand waved away or basically ignored by pretty much every historical discussion or documentary.
When you hear about Julius Caesar in Gaul: one third of the entire population was sold into slavery over the course of a few years.
The entire roman economy ran on slavery.
Spartacus is a staple of modern media thanks to Giovagnoli's novel and its translation into English but the brutality with which it and the other two "Slave wars" were put down in the space of 60 years are rarely touched on.