The parable of the widow’s mite (Luke 21:1-4) is that the poor widow who gave only a small amount to the treasury gave more than the rich who gave out of their abundance fits well with the economic theory of the declining marginal utility of money.  

The more money a person has, the less a new dollar of wealth adds to their wellbeing.  

By transferring resources from the wealthy to the less wealthy, the resources are placed with those who value them more.

The parable of the good Samaritan told of two men who knew that they should have helped another who had been robbed and wounded but did not, and a third man, who did not have an obligation, but did (Luke 10: 30-36).  

A progressive tax may force wealthy free-loaders who believe that aiding the poor is not their social responsibility to meet, the obligation that they wish to avoid.  

Add it all up and one could build a case for public policy to take that into consideration.

A true Christian couldn't object.