Evil begins when you begin to treat people as thingsWho said it
Terry Pratchett, the author of the Discworld series of comic fantasy novels.
I Shall Wear Midnight
Thoughts on the quote
Is there a universal morality? Many people think not. I think there is. For example, the Golden Rule and the Silver Rule have been around for 2,000 years, and there are variations in most other religions and philosophies.
In I Shall Wear Midnight (one of the great Tiffany Aching novels), Pratchett gives a definition of evil that could also be universal; it's another variation on the same theme as the two rules. But it is, in some ways, more explicit because it avoids the problems that different people like to be treated (or not treated) differently. But no one should be treated as a thing.
Treating people as things is also what a lot of evil people get fundamentally wrong. All people are people, all people deserve respect. No one should be treated as an object.
In addition, learning that other people are people like you is one of the landmarks in growing up.