If it is true that...

Current commercial & hobbyist dog breeders tend to select dogs for future breeding when quite young

and

Behavioral measures in breeding are more unstable & unreliable when the dog is young

Then it must be true that...

Current dog breeding practices are potentially dangerous on the genetic level

If it is true that...

Puppies need the proper stimuli to develop their genetic potentials

and

Current commercial & hobbyist dog breeders may not adequately provide the proper stimuli to puppies for them to develop their genetic potential

Then it must be true that...

Current dog breeding practices are potentially dangerous on the genetic level