The usual objection to raising taxes on the wealthy or
corporations is that such taxes undermine economic growth; yet there is
remarkably little evidence to back up those claims. Studies instead have
emphasized that neither business tax cuts [1] nor estate tax
cuts [2] play any significant role in local economic growth.
Instead, the sad truth is that almost every state tax
system requires working families to pay a higher percentage of their
income in taxes than their wealthier citizens. In fact, as the Institute on Taxation & Economic Policy
detailed in their 2003 study, Who
Pays?: [3] "[O]nly four states require their best-off citizens to pay
as much of their incomes in taxes as middle-income families have to
pay." As the graph below from ITEP shows, the average family
pays significantly more of their income in state taxes than the wealthy.

A report [4] by the Center on Budget and Policy Priorities and EPI emphasizes that making state tax systems more progressive is also a way to mitigate the broader trend of growing before-tax economic inequality.
Core Policies to Make Tax Systems More Progressive include:
General
Resources to Make Tax System More Progressive
- Institute
on Taxation and Economic Policy (ITEP) - Guide to Fair State and Local
Taxes [12]
- ITEP
- Who Pays? A Distributional Analysis of the Tax Systems in All 50
States [3]
- Progressive
States Network, Raising
Revenue Through Fair Taxes [13]
- Progressive
States Network - Dos
and Don'ts of Coping With State Budget Crises [14]
- Economic
Policy Institute - Rethinking
Growth Strategies [15]
- Center on Budget and Policy Priorities and EPI - Pulling Apart: A State-by-State Analysis of Income Trends [4]