Relevant Pratchett passage:

There is a very interesting debate raging at the moment about the nature of sin, for example,” said Oats.

“And what do they think? Against it, are they?” said Granny Weatherwax.

“It’s not as simple as that. It’s not a black and white issue. There are so many shades of gray.”

“Nope.”

"Pardon?”

“There’s no grays, only white that’s got grubby. I’m surprised you don’t know that. And sin, young man, is when you treat people as things. Including yourself. That’s what sin is.

"It’s a lot more complicated than that . . .”

“No. It ain’t. When people say things are a lot more complicated than that, they means they’re getting worried that they won’t like the truth. People as things, that’s where it starts.”

“Oh, I’m sure there are worse crimes . . .”

“But they starts with thinking about people as things . . . ”

— Terry Pratchett, Carpe Jugulum