The new parents of any child find assumptions challenged. But when you have an autistic child, the challenges are fundamental. Normal children are wired to understand social rules. They observe human behaviour intently, and they copy. They may ignore or disobey that voice, but that's a choice.
Autistic children have no such instinct, no such voice.
They cannot be tamed. Through a system of positive and negative reinforcement, desirable behaviours can be boosted and undesirable ones reduced, but this is training, not taming. Their powers of generalisation are limited. You can teach them not to bite their baby brother, but it won't stop them from sinking their teeth into anyone else's baby. They can't guess what you might be thinking.