What, precisely, fair taxation might be is a question often asked, and not always well answered.
We could always start with the idea that the amount of tax due is the amount the law says is due of course.
That debate could address issues about the tax base. Issues such as horizontal equity are relevant. Why is it that we now have a situation where income from capital is taxed so much less than income from work?
Because optimal tax theory says it should be.
And why are companies taxed less than the self employed?