Tax Splitting, money for rich at expense of poor

The proposed tax splitting laws which would enable a highly paid husband to split his official income with his wife, then pay a vastly reduced tax rate would reward the rich for having a stay at home parent, at the same time as poor beneficiary single parents are being forced into work ,or having their benefits cut. Beneficiaries pay an enormous secondary tax rate on anything that they earn. The $10,000 or so tax cut that John Key would receive under this new law, would be approximately the same as what a single parent with children is supposed to live on in a whole year.

Why should the mothering work performed by wives of rich employed partners be recognised as a contribution to society whereas the same work performed by poor single mothers on a benefit is not, and is only deemed "welfare dependency."?