Interesting question. Personally I won't let pups leave until 9 weeks if riding in a car, or 10 weeks if flying. Hopefully I can hold them until 10 to 12 weeks, but that is just my preference. Pups gain alot even after 8 weeks from being with their litter mates. The one's I have let leave at 8 have less confidence and have a harder time adjusting to the new home. And I DO think it's unethical to let them leave before 8 weeks, JMO! There are certain circumstances that people can't overcome and I do understand those, but for the majority those breeders seem to be out to make a buck- not caring about the individual puppy's well being.