Back to what you tell your children.

All our most deeply held values are beliefs, hard to back up with evidence. Most people teach the beliefs first, the reasoning afterwards.
You don't say "well I think it's wrong to hit your sister with a hammer, this is why, but you must make up your own mind" it's "PUT THAT HAMMER DOWN" maybe adding "or there will be consequences"
Logically it makes sense not to 'do as you would be done by' but to 'do what you can get away with' but even without being Theist most people think some things are right and try to instil those ideas in their children.