There's no guarantee that a "CO2 tax" would be equally distributed itself. For an extreme case, imagine if we put a universal CO2 tax on all products. A producer might chose to slash the price of luxury goods, instead funneling the cost to lower end options. That would cause the prices the poor pay to rise more than the you subsidy would offset.

Distributing the cost equally to the producer doesn't mean they carry over equally to consumer cost.