This is a really insensitive comment. As someone who's taken a few psychology classes, I can tell you that a "beating." doesn't translate into a "lesson.". The mind of a child literally cannot comprehend why they're being beaten so it only causes trauma due to them not understanding what it's even for.
Tough love is definitely abuse. Try that in IRL and I dare you to use that type of excuse in a court of law, that argument never works anywhere. I get where your coming from since Garp is a good person at heart but in from a criminal justice stand point that argument is stupid. Definitely could have used a better and more accurate analogy for Garp caring about his grand kids.
I respect your jabs as a degenerative asshole myself.