Every time a parent raises a hand to a child, the child learns that force is an acceptable substitute for reason, and that mom and dad have more confidence in force than in reason.
Corporal punishment also doesn’t work. In fact, it makes things worse. The research on this is compelling. A meta-analysis of 50 years of corporal punishment studies compiled by Elizabeth Gershoff at the University of Texas found 13 outcomes strongly correlated with corporal punishment, all of them negative. These include a damaged parent-child relationship, increased antisocial and aggressive behaviors and the increased likelihood that the spanked child will physically abuse his or her own children.
Earlier studies had found one positive outcome: immediate compliance. But the 2016 meta-analysis wiped out even that finding, showing that beatings have diminishing effectiveness over time. Kids become numb to it, they endure it and it ceases to even show that small, inadequate benefit.
So spanking eventually fails even in the primary goal of obedience.