A 17 month old can't be expected to have that much control over his emotions. That comes with age. He can be taught how to channel his feelings appropriately (and should be), but I don't think hitting the kid delivers that message at all. It's punishment, not discipline; and seems to usually be done as a means of stress relief for parents. I was spanked and it only changed my behavior in the short term. I never learned from it what the appropriate course of action would be.

And I feel sorry for the poor child who 'cries less' after being spanked at that age. It sounds like the child is withdrawing, learning to fear his parents, and being taught to bottle his emotions. In short - I believe your "friend" is full of bad advice.