The author is an f’ing idiot. Slavery was not a mistake. Slavery was a condition that had existed thousands of years and continues in parts of the world today. Our nation made the decision to end slavery and paid dearly for it.
The West has had a 133 year hiatus in the practice of slavery. When my grandparents were born in 1900, slavery had only been ended (peacefully, BTW) in Brazil for 12 years.
Slavery, like poverty and tyranny, is the norm. The fact that the West managed to suppress slavery (in the West...) for a 133 years is a colossal achievement.
But slavery is pretty obviously on the way back. All you have do is look at the ‘unaccompanied minors’ being smuggled in and guess at their likely fates...