They're fully grown adults in their thirties. They know what they're doing. I know plenty of people that were brought up by parents who thought it was perfectly OK to smack them as a punishment, but they have *not* gone on to do the same to their own children now because they know it's wrong. Also, it really is a simple as asking yourself whether you'd like to be showered with cold water in order to be taught a lesson. I'd guess that the vast majority of people wouldn't, so what makes it OK to do this to a defenceless baby? Plus, they have form. They're horrible parents in other ways, this is just one example tbh.