“Going out into the world without a good understanding of it defeats the whole purpose. It is like one sows without having plowed; the wind and birds will carry the seeds away, because they aren’t closed off and protected. So is he who merely reads Mussar like him who plants without a fence; pigs will eat and trample on everything. Some plant on stone. This is comparable to a heart of stone which cannot be penetrated unless it is struck until it breaks open. That’s why I wrote you to hit our children if they don’t obey you. “Train a lad in the way he ought to go” (Mishlei 22:6). This is an important principle of education.”
(Iggeres HaGr”a)
Now it may be claimed that times have changed and that the Torah has different interpretations for different times but that is an EXTREMELY slippery slope. And there are definitely contemporary, mainstream Gedolim who are of the opinion that it is valid today as it has always been. R’ Chaim Kanievsky for one. I personally heard him respond to a question posed to him – about educators in America who warn against ever hitting a child – with the one word response “Meshugaim”.