I hadn't heard about jail time as penalty, but am all for the law, for so many different reasons. One reason is that some parents have literally never heard that they should not hit their baby, and in fact think it is the responsible thing to do.
Also, it isn't inflicting punishment (jail time) to deter punishment per se, it is inflicting punishment for specifically assaulting a child. Just like when one assaults another adult they may go to jail.
~Tracy