Which human idea do you considered to be the most travesty that humanity has ever thought of?

I mean seriously why did humanity has to be so cruel back in the day and unfortunately stuff like these still going on.
Genocide
Slavery
Human Trafficking
Racism, Sexism, and Homophobia
Terrorist
Human Torture Devices
Select gender and age to cast your vote:
Which human idea do you considered to be the most travesty that humanity has ever thought of?
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