It is a social justice position. It is a preference. There is no right or wrong answer. It is important however to not let taxes at the margin get too high or it starts interfering with economic incentives to be productive, and starts killing the goose that lays the golden egg, as it were. It is an empirical question as to just how high a rate and where and when that really starts to be a drag.
You should examine your concept of social justice.
A tax that takes from one person to give it to another is stealing, pure and simple. It is as if you are saying that it is okay for you to jump over your fence at night and steal your neighbor's car because he has three and you only have one. Put that way, I hope it sounds ludicrous and that is exactly what a "progressive" tax is.
I understand that many people have a misbegotten notion of social justice unfortunately influenced by envy and Marxist philosophy, but I believe that social justice entails a WILLINGNESS on the part of the giver. Christ did not strip the rich young man of his fine clothes and posessions and give them to the poor, he told the young man to sell all that and give it to the poor. The difference is that it rested upon a free choice of the young man's to come to the aid of his fellow human beings, and social justice requires that we do the same.
Social justice does not require that we take someone's wealth at gunpoint and transfer it to another, no matter the other person's need or our good intentions.
"It is a social justice position"
You must have had a great time in college studying Karl Marx.
There. I fixed it.