Light physical punishment for children is like a string-on-an-elephant approach; it only works so long as they have the fear of punishment. In that sense, it's incredibly effective, in proper amounts and at proper times.
Abusive parents use it in improper amounts and at improper times. Lax parents smile while their children run around the supermarket screaming and vandalizing like a bunch of fucking nigger niglets.
There are moments in society where giving a stern talking to someone won't cut it; typically, the people in that situation either end up imprisoned, dead, maimed, or injured. It is better to teach them there are potential physical repercussions beyond grounding and single-mother-screeching tactics, when they are young and impressionable, than let them have the run of things and only chastise them verbally while they run amok where they eventually grow up and think they can break into someone's house without punishment and end up with two shells of double-ought buckshot in their chest.