The analogy between adults and children isn't perfect
I agree. How about we just make it about children? Is it ok for children to snack their friends?
Am I an abuser
Possibly
who needs criminalising and my children taken into care?
Depends how often and how hard. At the lowest level this law sends out an important message that hitting your child is never acceptable. (And it is hitting, no matter how much people prefer euphemisms like 'tap' or 'smack'.
Plenty of people bring up really nice children without hitting them.