Income inequality, underemployment and lack of employment opportunities are real problems. But words have meaning, and we as a species have had a pretty ugly history with slavery. Let’s not dilute the meaning of that word when there are others that are more accurate.
Experience demonstrates that there may be a slavery of wages only a little less galling and crushing in its effects than chattel slavery, and this slavery of wages must go down with the other.
Taking someone to task over the technically incorrect use of the word slavery seems a bit pedantic at best.