Okay.
When it comes to income splitting, you've got a two-parent family where one works and one doesn't and then you've got a two-parent family where both work. Why would it be fair to tax them differently in the sense that the whole purpose of the income splitting is to level the playing field when you have one parent who stays at home? It allows the two parents to average the income over two people, which is what two-parent families who both work do as well.
So why would that not make sense for a family that chooses to have one parent stay at home?