Based on Katherine Newman's book, "Taxing the Poor," Ezra Klein comments on how Southern states raise taxes in the most regressive fashion: through sales taxes that fall most heavily on the poor. Klein refers to a chart in the book that shows how state and local taxes vary by region:
As you can see, the South relies much more heavily on sales taxes and much less heavily on income taxes than the Northeast does. Sales taxes, of course, are regressive, while income taxes are progressive...
Being anti-tax doesn’t mean your state doesn’t need revenue. Instead, what it often means is that the composition of how you get that revenue ends up being more regressive. You tax goods more than incomes, slap higher user fees on the sorts of public services (buses, parks, libraries) that the poor use more than the rich, and generally try to raise money in ways your wealthier, more politically powerful constituents don’t notice.
Jonathan Chaitt broadens the thesis by looking at the nexus between taxation and political party throughout the country:
...Republican states tend to raise a far higher share of their taxes from the poor, and less from the rich, than Democratic states.
The South is the most reliant upon regressive sales taxes, followed by the West, followed by the Midwest, followed by the Northeast. The reverse is true of the property tax, which is progressive.
The basic picture here is that, at every level of government, the conservative movement fights for the most regressive possible distribution of the tax burden...
...When conservatives discuss the distribution of the tax burden, they tend to focus on the federal level (and even then they usually ignore the more regressive federal taxes.) But, of course, in our federal system, we divide the functions of government between the national, state, and local levels. Given that the latter two tend to charge higher rates to the poor -- especially in conservative states -- some level of progressivity at the national level is needed merely to keep the overall tax level flat.
The regressivity of state taxation is not unrelated to the need for progressive taxation at the national level. And it's not something that just happens, either. It's a vital element of conservative policy, one which conservatives will go to great lengths to defend in the rare instances when it's challenged.