Be it +ve or -ve it is still discrimination. Tax code is used by governments to categorize its citizens to make tax collecting easy. But that in itself is already flawed because you are using people's features, last names, yearly income, marital status etc etc to cateegorize the society. By doing so you have already discriminated people. All the flat nosed ones in one side, all the divorsed in another, all the hindus, all the six figure salaries in another... etc etc