A fair tax system is a progressive one. Not every tax has to be progressive, but, overall, the tax system should be progressive. That means that people with higher incomes should pay a bit more as a percentage of their incomes in tax and they shouldn't pay less. I've heard people complain that this is unfair to people earning higher incomes; in fact, the reverse is currently true. Middle-income people currently pay a higher overall rate of tax than higher-income people when GST is taken into account.