And also because he's five and five year olds *really like having consistent rules*. They aren't even always happy when you break or bend the rules to their benefit.

But I'd love more detail from LW here, because there's a big difference between a kid "tattling" that their sister got a cookie before lunch without asking (if that's allowed) and a kid tattling that their sister took their cookie and ate it and LW going "Solve it yourself, you're supposed to be learning independence".

And while your interpretation is certainly the more plausible, we've all known terrible adults whose response to bullying or meanness is "Sticks and stones, kiddo" and "You need to learn to stand up for yourself!" and the like.